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Tag: Caltech/MIT Advanced aLigo
From “Science Alert (AU)” : “Uncanny Coincidence – Fast Radio Burst Detected After Gravitational Wave Event”
Artist’s impression of a neutron star collision. (L. Calçada/M. Kornmesser/ESO)
Every so often, a strange signal from outer space hits our detectors here on Earth.
Known as fast radio bursts (FRBs_, these signals are extremely short, just milliseconds in duration, and are detected only in radio wavelengths.
Yet in those milliseconds, and in those wavelengths, they can discharge as much energy as 500 million Suns – and most of them have never been detected again.
What they are, and how they are generated, is something of a baffling mystery. But a new discovery could point to a previously unknown mechanism producing these powerful bursts of radiation.
On the 25th of April in 2019, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) recorded a bright, non-repeating fast radio burst ( FRB).
Just 2.5 hours earlier, the Laser Interferometer Gravitational-Wave Observatory (LIGO) recorded a gravitational wave event, the collision as a binary neutron star reached the inevitable conclusion of its decaying orbit.
The FRB’s location in the sky fell within the credible region of the gravitational wave event, and from a similar distance. The chance that the two events were unrelated, a team of astronomers led by Alexandra Moroianu of the University of Western Australia has determined, is extremely small.
FRBs are extremely enigmatic; only a few of them repeat, and the one-off nature of the vast majority makes them extraordinarily difficult to study.
Their detection used to be chance only; you had to be studying the right patch of the sky at the right time to catch one. All-sky surveys, however, have increased the number of detections to over 600.
A breakthrough came in 2020: for the first time, an FRB was detected coming from within the Milky Way galaxy. It was traced to a type of neutron star called a magnetar, whose insanely powerful external magnetic field fights against the inward pull of gravity, causing the star to occasionally quake and flare.
But while misbehaving magnetars present one explanation, we don’t know if that’s the whole picture. FRBs vary quite a bit, and it’s likely that there’s more than one mechanism that can produce them.
There are several theories that predict an association between FRBs and gravitational waves, particularly if neutron stars are involved, either during or following the gravitational wave detection.
So Moroianu and her colleagues went looking in catalogs. The CHIME catalog of observations from July 2018 to July 2019 overlapped with the LIGO-Virgo observation run, for a total of 171 FRB events.
The researchers cross-referenced these events with the GWTC-2 catalog, looking for FRB events that occurred temporally close to gravitational wave detections, within the patch of the sky identified by LIGO.
And they got a very palpable hit.
The cyan spot represents FRB20190425A. The red-orange regions represent the part of the sky from which GW20190425 could have emerged. (Moroianu et al., Nature Astronomy, 2023)
GW20190425 was observed by LIGO on 25 April 2019 at 18:18:05 UTC. The absence of a detection by the Virgo detector helped constrain the region from which the detection had emerged. Its estimated distance was around 520 million light-years away, generated by a merger between two neutron stars.
FRB20190425A was detected the same day, at 10:46:33 UTC, within the range of sky LIGO had laid out as a plausible source of the neutron star merger, and with an upper distance limit of 590 million light-years.
This, they found, would be an uncanny coincidence if the two were unrelated. The probability of the two events occurring at the distances given, the timeframe of detection, and within the region of space defined by LIGO was just 0.00019, the researchers calculated.
The two events likely emerged from a galaxy called UGC 10667, but the mechanism that produced the FRB might take a little more analysis.
For now, the team believes that the burst was caused by a blitzar, a mechanism proposed for FRBs nearly a decade ago. This is when a neutron star too massive to remain supported by degeneracy pressure collapses into a black hole when its spin slows – the only thing that was preventing this collapse.
“Although we cannot definitively assign the potential GW-FRB association to a single theory, it is consistent with the GW, short gamma-ray burst (sGRB) and FRB association theory that invokes the collapse of a post-binary neutron star-merger magnetar,” the researchers write.
“The FRB generation mechanism is the so-called blitzar mechanism, which has been confirmed through numerical simulations. Within this scenario, the 2.5-hour delay time between the FRB and the GW event is the survival time of the supramassive neutron star before collapsing into a black hole, which is consistent with the expected range of the delay timescale for a supramassive magnetar from both theory and observational data.”
The masses of the neutron stars of GW20190425 were significantly higher than most neutron star binaries detected in the Milky Way. These lower mass binaries would produce more stable heavyweight neutron stars after they merge, which could survive a long time and repeatedly spit out FRBs, thus explaining the few repeating FRB sources.
Whether or not the two events were linked remains to be confirmed, but one thing is certain: the estimated rate of binary neutron star mergers is far, far lower than the rate at which FRBs like FRB190425A are detected. So this potential mechanism cannot, alone, account for the mysterious signals that sputter across the radio sky.
Further investigation is still warranted. But it’s tremendously exciting that we seem to be closing in on some answers.
The research has been published in Nature Astronomy.
Numerical simulation of the neutron stars merging to form a black hole, with their accretion disks interacting to produce electromagnetic waves. Credit: L. Rezolla (AEI) & M. Koppitz (AEI & Zuse-Institut Berlin)
Scientists have advanced in discovering how to use ripples in space-time known as gravitational waves to peer back to the beginning of everything we know.
The researchers say they can better understand the state of the cosmos shortly after the Big Bang by learning how these ripples in the fabric of the universe flow through planets and the gas between the galaxies.
“We can’t see the early universe directly, but maybe we can see it indirectly if we look at how gravitational waves from that time have affected matter and radiation that we can observe today,” said Deepen Garg, lead author of a paper
reporting the results in the Journal of Cosmology and Astroparticle Physics [below]. Garg is a graduate student in the Princeton Program in Plasma Physics, which is based at the DOE’s Princeton Plasma Physics Laboratory (PPPL).
Garg and his advisor Ilya Dodin, who is affiliated with both Princeton University and PPPL, adapted this technique from their research into fusion energy, the process powering the sun and stars that scientists are developing to create electricity on Earth without emitting greenhouse gases or producing long-lived radioactive waste. Fusion scientists calculate how electromagnetic waves move through plasma, the soup of electrons and atomic nuclei that fuels fusion facilities known as tokamaks and stellarators.
It turns out that this process resembles the movement of gravitational waves through matter. “We basically put plasma wave machinery to work on a gravitational wave problem,” Garg said.
Gravitational waves, first predicted by Albert Einstein in 1916 as a consequence of his General Theory of Relativity, are disturbances in space-time caused by the movement of very dense objects. They travel at the speed of light and were first detected in 2015 by the Laser Interferometer Gravitational Wave Observatory (LIGO) through detectors in Washington State and Louisiana.
Garg and Dodin created formulas that could theoretically lead gravitational waves to reveal hidden properties about celestial bodies, like stars that are many light years away. As the waves flow through matter, they create light whose characteristics depend on the matter’s density.
A physicist could analyze that light and discover properties about a star millions of light years away. This technique could also lead to discoveries about the smashing together of neutron stars and black holes, ultra-dense remnants of star deaths. They could even potentially reveal information about what was happening during the Big Bang and the early moments of our universe.
The research began without any sense of how important it might become. “I thought this would be a small, six-month project for a graduate student that would involve solving something simple,” Dodin said. “But once we started digging deeper into the topic, we realized that very little was understood about the problem and we could do some very basic theory work here.”
The scientists now plan to use the technique to analyze data in the near future. “We have some formulas now, but getting meaningful results will take more work,” Garg said.
The Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University. PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit https://energy.gov/science.
About Princeton: Overview
Princeton University is a private Ivy League research university in Princeton, New Jersey (US). Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the nine colonial colleges chartered before the American Revolution. The institution moved to Newark in 1747, then to the current site nine years later. It was renamed Princeton University in 1896.
Princeton provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences, and engineering. It offers professional degrees through the Princeton School of Public and International Affairs, the School of Engineering and Applied Science, the School of Architecture and the Bendheim Center for Finance. The university also manages the DOE’s Princeton Plasma Physics Laboratory. Princeton has the largest endowment per student in the United States.
As of October 2020, 69 Nobel laureates, 15 Fields Medalists and 14 Turing Award laureates have been affiliated with Princeton University as alumni, faculty members or researchers. In addition, Princeton has been associated with 21 National Medal of Science winners, 5 Abel Prize winners, 5 National Humanities Medal recipients, 215 Rhodes Scholars, 139 Gates Cambridge Scholars and 137 Marshall Scholars. Two U.S. Presidents, twelve U.S. Supreme Court Justices (three of whom currently serve on the court) and numerous living billionaires and foreign heads of state are all counted among Princeton’s alumni body. Princeton has also graduated many prominent members of the U.S. Congress and the U.S. Cabinet, including eight Secretaries of State, three Secretaries of Defense and the current Chairman of the Joint Chiefs of Staff.
Princeton University, founded as the College of New Jersey, was considered the successor of the “Log College” founded by the Reverend William Tennent at Neshaminy, PA in about 1726. New Light Presbyterians founded the College of New Jersey in 1746 in Elizabeth, New Jersey. Its purpose was to train ministers. The college was the educational and religious capital of Scottish Presbyterian America. Unlike Harvard University , which was originally “intensely English” with graduates taking the side of the crown during the American Revolution, Princeton was founded to meet the religious needs of the period and many of its graduates took the American side in the war. In 1754, trustees of the College of New Jersey suggested that, in recognition of Governor Jonathan Belcher’s interest, Princeton should be named as Belcher College. Belcher replied: “What a name that would be!” In 1756, the college moved its campus to Princeton, New Jersey. Its home in Princeton was Nassau Hall, named for the royal House of Orange-Nassau of William III of England.
Following the untimely deaths of Princeton’s first five presidents, John Witherspoon became president in 1768 and remained in that post until his death in 1794. During his presidency, Witherspoon shifted the college’s focus from training ministers to preparing a new generation for secular leadership in the new American nation. To this end, he tightened academic standards and solicited investment in the college. Witherspoon’s presidency constituted a long period of stability for the college, interrupted by the American Revolution and particularly the Battle of Princeton, during which British soldiers briefly occupied Nassau Hall; American forces, led by George Washington, fired cannon on the building to rout them from it.
In 1812, the eighth president of the College of New Jersey, Ashbel Green (1812–23), helped establish the Princeton Theological Seminary next door. The plan to extend the theological curriculum met with “enthusiastic approval on the part of the authorities at the College of New Jersey.” Today, Princeton University and Princeton Theological Seminary maintain separate institutions with ties that include services such as cross-registration and mutual library access.
Before the construction of Stanhope Hall in 1803, Nassau Hall was the college’s sole building. The cornerstone of the building was laid on September 17, 1754. During the summer of 1783, the Continental Congress met in Nassau Hall, making Princeton the country’s capital for four months. Over the centuries and through two redesigns following major fires (1802 and 1855), Nassau Hall’s role shifted from an all-purpose building, comprising office, dormitory, library, and classroom space; to classroom space exclusively; to its present role as the administrative center of the University. The class of 1879 donated twin lion sculptures that flanked the entrance until 1911, when that same class replaced them with tigers. Nassau Hall’s bell rang after the hall’s construction; however, the fire of 1802 melted it. The bell was then recast and melted again in the fire of 1855.
James McCosh became the college’s president in 1868 and lifted the institution out of a low period that had been brought about by the American Civil War. During his two decades of service, he overhauled the curriculum, oversaw an expansion of inquiry into the sciences, and supervised the addition of a number of buildings in the High Victorian Gothic style to the campus. McCosh Hall is named in his honor.
In 1879, the first thesis for a Doctor of Philosophy (Ph.D.) was submitted by James F. Williamson, Class of 1877.
In 1896, the college officially changed its name from the College of New Jersey to Princeton University to honor the town in which it resides. During this year, the college also underwent large expansion and officially became a university. In 1900, the Graduate School was established.
In 1902, Woodrow Wilson, graduate of the Class of 1879, was elected the 13th president of the university. Under Wilson, Princeton introduced the preceptorial system in 1905, a then-unique concept in the United States that augmented the standard lecture method of teaching with a more personal form in which small groups of students, or precepts, could interact with a single instructor, or preceptor, in their field of interest.
In 1906, the reservoir Carnegie Lake was created by Andrew Carnegie. A collection of historical photographs of the building of the lake is housed at the Seeley G. Mudd Manuscript Library on Princeton’s campus. On October 2, 1913, the Princeton University Graduate College was dedicated. In 1919 the School of Architecture was established. In 1933, Albert Einstein became a lifetime member of the Institute for Advanced Study with an office on the Princeton campus. While always independent of the university, the Institute for Advanced Study occupied offices in Jones Hall for 6 years, from its opening in 1933, until its own campus was finished and opened in 1939.
Coeducation
In 1969, Princeton University first admitted women as undergraduates. In 1887, the university actually maintained and staffed a sister college, Evelyn College for Women, in the town of Princeton on Evelyn and Nassau streets. It was closed after roughly a decade of operation. After abortive discussions with Sarah Lawrence College to relocate the women’s college to Princeton and merge it with the University in 1967, the administration decided to admit women and turned to the issue of transforming the school’s operations and facilities into a female-friendly campus. The administration had barely finished these plans in April 1969 when the admissions office began mailing out its acceptance letters. Its five-year coeducation plan provided $7.8 million for the development of new facilities that would eventually house and educate 650 women students at Princeton by 1974. Ultimately, 148 women, consisting of 100 freshmen and transfer students of other years, entered Princeton on September 6, 1969 amidst much media attention. Princeton enrolled its first female graduate student, Sabra Follett Meservey, as a PhD candidate in Turkish history in 1961. A handful of undergraduate women had studied at Princeton from 1963 on, spending their junior year there to study “critical languages” in which Princeton’s offerings surpassed those of their home institutions. They were considered regular students for their year on campus, but were not candidates for a Princeton degree.
As a result of a 1979 lawsuit by Sally Frank, Princeton’s eating clubs were required to go coeducational in 1991, after Tiger Inn’s appeal to the U.S. Supreme Court was denied. In 1987, the university changed the gendered lyrics of “Old Nassau” to reflect the school’s co-educational student body. From 2009 to 2011, Princeton professor Nannerl O. Keohane chaired a committee on undergraduate women’s leadership at the university, appointed by President Shirley M. Tilghman.
The main campus sits on about 500 acres (2.0 km^2) in Princeton. In 2011, the main campus was named by Travel+Leisure as one of the most beautiful in the United States. The James Forrestal Campus is split between nearby Plainsboro and South Brunswick. The University also owns some property in West Windsor Township. The campuses are situated about one hour from both New York City and Philadelphia.
The first building on campus was Nassau Hall, completed in 1756 and situated on the northern edge of campus facing Nassau Street. The campus expanded steadily around Nassau Hall during the early and middle 19th century. The McCosh presidency (1868–88) saw the construction of a number of buildings in the High Victorian Gothic and Romanesque Revival styles; many of them are now gone, leaving the remaining few to appear out of place. At the end of the 19th century much of Princeton’s architecture was designed by the Cope and Stewardson firm (same architects who designed a large part of Washington University in St Louis and University of Pennsylvania) resulting in the Collegiate Gothic style for which it is known today. Implemented initially by William Appleton Potter and later enforced by the University’s supervising architect, Ralph Adams Cram, the Collegiate Gothic style remained the standard for all new building on the Princeton campus through 1960. A flurry of construction in the 1960s produced a number of new buildings on the south side of the main campus, many of which have been poorly received. Several prominent architects have contributed some more recent additions, including Frank Gehry (Lewis Library), I. M. Pei (Spelman Halls), Demetri Porphyrios (Whitman College, a Collegiate Gothic project), Robert Venturi and Denise Scott Brown (Frist Campus Center, among several others), and Rafael Viñoly (Carl Icahn Laboratory).
A group of 20th-century sculptures scattered throughout the campus forms the Putnam Collection of Sculpture. It includes works by Alexander Calder (Five Disks: One Empty), Jacob Epstein (Albert Einstein), Henry Moore (Oval with Points), Isamu Noguchi (White Sun), and Pablo Picasso (Head of a Woman). Richard Serra’s The Hedgehog and The Fox is located between Peyton and Fine halls next to Princeton Stadium and the Lewis Library.
At the southern edge of the campus is Carnegie Lake, an artificial lake named for Andrew Carnegie. Carnegie financed the lake’s construction in 1906 at the behest of a friend who was a Princeton alumnus. Carnegie hoped the opportunity to take up rowing would inspire Princeton students to forsake football, which he considered “not gentlemanly.” The Shea Rowing Center on the lake’s shore continues to serve as the headquarters for Princeton rowing.
Cannon Green
Buried in the ground at the center of the lawn south of Nassau Hall is the “Big Cannon,” which was left in Princeton by British troops as they fled following the Battle of Princeton. It remained in Princeton until the War of 1812, when it was taken to New Brunswick. In 1836 the cannon was returned to Princeton and placed at the eastern end of town. It was removed to the campus under cover of night by Princeton students in 1838 and buried in its current location in 1840.
A second “Little Cannon” is buried in the lawn in front of nearby Whig Hall. This cannon, which may also have been captured in the Battle of Princeton, was stolen by students of Rutgers University in 1875. The theft ignited the Rutgers-Princeton Cannon War. A compromise between the presidents of Princeton and Rutgers ended the war and forced the return of the Little Cannon to Princeton. The protruding cannons are occasionally painted scarlet by Rutgers students who continue the traditional dispute.
In years when the Princeton football team beats the teams of both Harvard University and Yale University in the same season, Princeton celebrates with a bonfire on Cannon Green. This occurred in 2012, ending a five-year drought. The next bonfire happened on November 24, 2013, and was broadcast live over the Internet.
Landscape
Princeton’s grounds were designed by Beatrix Farrand between 1912 and 1943. Her contributions were most recently recognized with the naming of a courtyard for her. Subsequent changes to the landscape were introduced by Quennell Rothschild & Partners in 2000. In 2005, Michael Van Valkenburgh was hired as the new consulting landscape architect for the campus. Lynden B. Miller was invited to work with him as Princeton’s consulting gardening architect, focusing on the 17 gardens that are distributed throughout the campus.
Buildings
Nassau Hall
Nassau Hall is the oldest building on campus. Begun in 1754 and completed in 1756, it was the first seat of the New Jersey Legislature in 1776, was involved in the battle of Princeton in 1777, and was the seat of the Congress of the Confederation (and thus capitol of the United States) from June 30, 1783, to November 4, 1783. It now houses the office of the university president and other administrative offices, and remains the symbolic center of the campus. The front entrance is flanked by two bronze tigers, a gift of the Princeton Class of 1879. Commencement is held on the front lawn of Nassau Hall in good weather. In 1966, Nassau Hall was added to the National Register of Historic Places.
Residential colleges
Princeton has six undergraduate residential colleges, each housing approximately 500 freshmen, sophomores, some juniors and seniors, and a handful of junior and senior resident advisers. Each college consists of a set of dormitories, a dining hall, a variety of other amenities—such as study spaces, libraries, performance spaces, and darkrooms—and a collection of administrators and associated faculty. Two colleges, First College and Forbes College (formerly Woodrow Wilson College and Princeton Inn College, respectively), date to the 1970s; three others, Rockefeller, Mathey, and Butler Colleges, were created in 1983 following the Committee on Undergraduate Residential Life (CURL) report, which suggested the institution of residential colleges as a solution to an allegedly fragmented campus social life. The construction of Whitman College, the university’s sixth residential college, was completed in 2007.
Rockefeller and Mathey are located in the northwest corner of the campus; Princeton brochures often feature their Collegiate Gothic architecture. Like most of Princeton’s Gothic buildings, they predate the residential college system and were fashioned into colleges from individual dormitories.
First and Butler, located south of the center of the campus, were built in the 1960s. First served as an early experiment in the establishment of the residential college system. Butler, like Rockefeller and Mathey, consisted of a collection of ordinary dorms (called the “New New Quad”) before the addition of a dining hall made it a residential college. Widely disliked for their edgy modernist design, including “waffle ceilings,” the dormitories on the Butler Quad were demolished in 2007. Butler is now reopened as a four-year residential college, housing both under- and upperclassmen.
Forbes is located on the site of the historic Princeton Inn, a gracious hotel overlooking the Princeton golf course. The Princeton Inn, originally constructed in 1924, played regular host to important symposia and gatherings of renowned scholars from both the university and the nearby Institute for Advanced Study for many years. Forbes currently houses nearly 500 undergraduates in its residential halls.
In 2003, Princeton broke ground for a sixth college named Whitman College after its principal sponsor, Meg Whitman, who graduated from Princeton in 1977. The new dormitories were constructed in the Collegiate Gothic architectural style and were designed by architect Demetri Porphyrios. Construction finished in 2007, and Whitman College was inaugurated as Princeton’s sixth residential college that same year.
The precursor of the present college system in America was originally proposed by university president Woodrow Wilson in the early 20th century. For over 800 years, however, the collegiate system had already existed in Britain at University of Cambridge (UK) and University of Oxford (UK). Wilson’s model was much closer to Yale University’s present system, which features four-year colleges. Lacking the support of the trustees, the plan languished until 1968. That year, Wilson College was established to cap a series of alternatives to the eating clubs. Fierce debates raged before the present residential college system emerged. The plan was first attempted at Yale, but the administration was initially uninterested; an exasperated alumnus, Edward Harkness, finally paid to have the college system implemented at Harvard in the 1920s, leading to the oft-quoted aphorism that the college system is a Princeton idea that was executed at Harvard with funding from Yale.
Princeton has one graduate residential college, known simply as the Graduate College, located beyond Forbes College at the outskirts of campus. The far-flung location of the GC was the spoil of a squabble between Woodrow Wilson and then-Graduate School Dean Andrew Fleming West. Wilson preferred a central location for the college; West wanted the graduate students as far as possible from the campus. Ultimately, West prevailed. The Graduate College is composed of a large Collegiate Gothic section crowned by Cleveland Tower, a local landmark that also houses a world-class carillon. The attached New Graduate College provides a modern contrast in architectural style.
McCarter Theatre
The Tony-award-winning McCarter Theatre was built by the Princeton Triangle Club, a student performance group, using club profits and a gift from Princeton University alumnus Thomas McCarter. Today, the Triangle Club performs its annual freshmen revue, fall show, and Reunions performances in McCarter. McCarter is also recognized as one of the leading regional theaters in the United States.
Art Museum
The Princeton University Art Museum was established in 1882 to give students direct, intimate, and sustained access to original works of art that complement and enrich instruction and research at the university. This continues to be a primary function, along with serving as a community resource and a destination for national and international visitors.
Numbering over 92,000 objects, the collections range from ancient to contemporary art and concentrate geographically on the Mediterranean regions, Western Europe, China, the United States, and Latin America. There is a collection of Greek and Roman antiquities, including ceramics, marbles, bronzes, and Roman mosaics from faculty excavations in Antioch. Medieval Europe is represented by sculpture, metalwork, and stained glass. The collection of Western European paintings includes examples from the early Renaissance through the 19th century, with masterpieces by Monet, Cézanne, and Van Gogh, and features a growing collection of 20th-century and contemporary art, including iconic paintings such as Andy Warhol’s Blue Marilyn.
One of the best features of the museums is its collection of Chinese art, with important holdings in bronzes, tomb figurines, painting, and calligraphy. Its collection of pre-Columbian art includes examples of Mayan art, and is commonly considered to be the most important collection of pre-Columbian art outside of Latin America. The museum has collections of old master prints and drawings and a comprehensive collection of over 27,000 original photographs. African art and Northwest Coast Indian art are also represented. The Museum also oversees the outdoor Putnam Collection of Sculpture.
University Chapel
The Princeton University Chapel is located on the north side of campus, near Nassau Street. It was built between 1924 and 1928, at a cost of $2.3 million [approximately $34.2 million in 2020 dollars]. Ralph Adams Cram, the University’s supervising architect, designed the chapel, which he viewed as the crown jewel for the Collegiate Gothic motif he had championed for the campus. At the time of its construction, it was the second largest university chapel in the world, after King’s College Chapel, Cambridge. It underwent a two-year, $10 million restoration campaign between 2000 and 2002.
Measured on the exterior, the chapel is 277 feet (84 m) long, 76 feet (23 m) wide at its transepts, and 121 feet (37 m) high. The exterior is Pennsylvania sandstone, with Indiana limestone used for the trim. The interior is mostly limestone and Aquia Creek sandstone. The design evokes an English church of the Middle Ages. The extensive iconography, in stained glass, stonework, and wood carvings, has the common theme of connecting religion and scholarship.
The Chapel seats almost 2,000. It hosts weekly ecumenical Christian services, daily Roman Catholic mass, and several annual special events.
Murray-Dodge Hall
Murray-Dodge Hall houses the Office of Religious Life (ORL), the Murray Dodge Theater, the Murray-Dodge Café, the Muslim Prayer Room and the Interfaith Prayer Room. The ORL houses the office of the Dean of Religious Life, Alison Boden, and a number of university chaplains, including the country’s first Hindu chaplain, Vineet Chander; and one of the country’s first Muslim chaplains, Sohaib Sultan.
Sustainability
Published in 2008, Princeton’s Sustainability Plan highlights three priority areas for the University’s Office of Sustainability: reduction of greenhouse gas emissions; conservation of resources; and research, education, and civic engagement. Princeton has committed to reducing its carbon dioxide emissions to 1990 levels by 2020: Energy without the purchase of offsets. The University published its first Sustainability Progress Report in November 2009. The University has adopted a green purchasing policy and recycling program that focuses on paper products, construction materials, lightbulbs, furniture, and electronics. Its dining halls have set a goal to purchase 75% sustainable food products by 2015. The student organization “Greening Princeton” seeks to encourage the University administration to adopt environmentally friendly policies on campus.
Organization
The Trustees of Princeton University, a 40-member board, is responsible for the overall direction of the University. It approves the operating and capital budgets, supervises the investment of the University’s endowment and oversees campus real estate and long-range physical planning. The trustees also exercise prior review and approval concerning changes in major policies, such as those in instructional programs and admission, as well as tuition and fees and the hiring of faculty members.
With an endowment of $26.1 billion, Princeton University is among the wealthiest universities in the world. Ranked in 2010 as the third largest endowment in the United States, the university had the greatest per-student endowment in the world (over $2 million for undergraduates) in 2011. Such a significant endowment is sustained through the continued donations of its alumni and is maintained by investment advisers. Some of Princeton’s wealth is invested in its art museum, which features works by Claude Monet, Vincent van Gogh, Jackson Pollock, and Andy Warhol among other prominent artists.
Academics
Undergraduates fulfill general education requirements, choose among a wide variety of elective courses, and pursue departmental concentrations and interdisciplinary certificate programs. Required independent work is a hallmark of undergraduate education at Princeton. Students graduate with either the Bachelor of Arts (A.B.) or the Bachelor of Science in Engineering (B.S.E.).
The graduate school offers advanced degrees spanning the humanities, social sciences, natural sciences, and engineering. Doctoral education is available in most disciplines. It emphasizes original and independent scholarship whereas master’s degree programs in architecture, engineering, finance, and public affairs and public policy prepare candidates for careers in public life and professional practice.
Undergraduate courses in the humanities are traditionally either seminars or lectures held 2 or 3 times a week with an additional discussion seminar that is called a “precept.” To graduate, all A.B. candidates must complete a senior thesis and, in most departments, one or two extensive pieces of independent research that are known as “junior papers.” Juniors in some departments, including architecture and the creative arts, complete independent projects that differ from written research papers. A.B. candidates must also fulfill a three or four semester foreign language requirement and distribution requirements (which include, for example, classes in ethics, literature and the arts, and historical analysis) with a total of 31 classes. B.S.E. candidates follow a parallel track with an emphasis on a rigorous science and math curriculum, a computer science requirement, and at least two semesters of independent research including an optional senior thesis. All B.S.E. students must complete at least 36 classes. A.B. candidates typically have more freedom in course selection than B.S.E. candidates because of the fewer number of required classes. Nonetheless, in the spirit of a liberal arts education, both enjoy a comparatively high degree of latitude in creating a self-structured curriculum.
Undergraduates agree to adhere to an academic integrity policy called the Honor Code, established in 1893. Under the Honor Code, faculty do not proctor examinations; instead, the students proctor one another and must report any suspected violation to an Honor Committee made up of undergraduates. The Committee investigates reported violations and holds a hearing if it is warranted. An acquittal at such a hearing results in the destruction of all records of the hearing; a conviction results in the student’s suspension or expulsion. The signed pledge required by the Honor Code is so integral to students’ academic experience that the Princeton Triangle Club performs a song about it each fall. Out-of-class exercises fall under the jurisdiction of the Faculty-Student Committee on Discipline. Undergraduates are expected to sign a pledge on their written work affirming that they have not plagiarized the work.
Graduate
The Graduate School has about 2,600 students in 42 academic departments and programs in social sciences; engineering; natural sciences; and humanities. These departments include the Department of Psychology; Department of History; and Department of Economics.
In 2017–2018, it received nearly 11,000 applications for admission and accepted around 1,000 applicants. The University also awarded 319 Ph.D. degrees and 170 final master’s degrees. Princeton has no medical school, law school, business school, or school of education. (A short-lived Princeton Law School folded in 1852.) It offers professional graduate degrees in architecture; engineering; finance and public policy- the last through the Princeton School of Public and International Affairs founded in 1930 as the School of Public and International Affairs and renamed in 1948 after university president (and U.S. president) Woodrow Wilson, and most recently renamed in 2020.
Libraries
The Princeton University Library system houses over eleven million holdings including seven million bound volumes. The main university library, Firestone Library, which houses almost four million volumes, is one of the largest university libraries in the world. Additionally, it is among the largest “open stack” libraries in existence. Its collections include the autographed manuscript of F. Scott Fitzgerald’s The Great Gatsby and George F. Kennan’s Long Telegram. In addition to Firestone library, specialized libraries exist for architecture, art and archaeology, East Asian studies, engineering, music, public and international affairs, public policy and university archives, and the sciences. In an effort to expand access, these libraries also subscribe to thousands of electronic resources.
Institutes
High Meadows Environmental Institute
The High Meadows Environmental Institute is an “interdisciplinary center of environmental research, education, and outreach” at the university. The institute was started in 1994. About 90 faculty members at Princeton University are affiliated with it.
The High Meadows Environmental Institute has the following research centers:
Carbon Mitigation Initiative (CMI): This is a 15-year-long partnership between PEI and British Petroleum with the goal of finding solutions to problems related to climate change. The Stabilization Wedge Game has been created as part of this initiative.
Center for BioComplexity (CBC)
Cooperative Institute for Climate Science (CICS): This is a collaboration with the National Oceanographic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory.
Energy Systems Analysis Group
Grand Challenges
The DOE’s Princeton Plasma Physics Laboratory was founded in 1951 as Project Matterhorn, a top-secret cold war project aimed at achieving controlled nuclear fusion. Princeton astrophysics professor Lyman Spitzer became the first director of the project and remained director until the lab’s declassification in 1961 when it received its current name.
PPPL currently houses approximately half of the graduate astrophysics department, the Princeton Program in Plasma Physics. The lab is also home to the Harold P. Furth Plasma Physics Library. The library contains all declassified Project Matterhorn documents, included the first design sketch of a stellarator by Lyman Spitzer.
Princeton is one of five US universities to have and to operate a Department of Energy national laboratory.
Student life and culture
University housing is guaranteed to all undergraduates for all four years. More than 98% of students live on campus in dormitories. Freshmen and sophomores must live in residential colleges, while juniors and seniors typically live in designated upperclassman dormitories. The actual dormitories are comparable, but only residential colleges have dining halls. Nonetheless, any undergraduate may purchase a meal plan and eat in a residential college dining hall. Recently, upperclassmen have been given the option of remaining in their college for all four years. Juniors and seniors also have the option of living off-campus, but high rent in the Princeton area encourages almost all students to live in university housing. Undergraduate social life revolves around the residential colleges and a number of coeducational eating clubs, which students may choose to join in the spring of their sophomore year. Eating clubs, which are not officially affiliated with the university, serve as dining halls and communal spaces for their members and also host social events throughout the academic year.
Princeton’s six residential colleges host a variety of social events and activities, guest speakers, and trips. The residential colleges also sponsor trips to New York for undergraduates to see ballets, operas, Broadway shows, sports events, and other activities. The eating clubs, located on Prospect Avenue, are co-ed organizations for upperclassmen. Most upperclassmen eat their meals at one of the eleven eating clubs. Additionally, the clubs serve as evening and weekend social venues for members and guests. The eleven clubs are Cannon; Cap and Gown; Charter; Cloister; Colonial; Cottage; Ivy; Quadrangle; Terrace; Tiger; and Tower.
Princeton hosts two Model United Nations conferences, PMUNC in the fall for high school students and PDI in the spring for college students. It also hosts the Princeton Invitational Speech and Debate tournament each year at the end of November. Princeton also runs Princeton Model Congress, an event that is held once a year in mid-November. The four-day conference has high school students from around the country as participants.
Although the school’s admissions policy is need-blind, Princeton, based on the proportion of students who receive Pell Grants, was ranked as a school with little economic diversity among all national universities ranked by U.S. News & World Report. While Pell figures are widely used as a gauge of the number of low-income undergraduates on a given campus, the rankings article cautions “the proportion of students on Pell Grants isn’t a perfect measure of an institution’s efforts to achieve economic diversity,” but goes on to say that “still, many experts say that Pell figures are the best available gauge of how many low-income undergrads there are on a given campus.”
TigerTrends is a university-based student run fashion, arts, and lifestyle magazine.
Demographics
Princeton has made significant progress in expanding the diversity of its student body in recent years. The 2019 freshman class was one of the most diverse in the school’s history, with 61% of students identifying as students of color. Undergraduate and master’s students were 51% male and 49% female for the 2018–19 academic year.
The median family income of Princeton students is $186,100, with 57% of students coming from the top 10% highest-earning families and 14% from the bottom 60%.
In 1999, 10% of the student body was Jewish, a percentage lower than those at other Ivy League schools. Sixteen percent of the student body was Jewish in 1985; the number decreased by 40% from 1985 to 1999. This decline prompted The Daily Princetonian to write a series of articles on the decline and its reasons. Caroline C. Pam of The New York Observer wrote that Princeton was “long dogged by a reputation for anti-Semitism” and that this history as well as Princeton’s elite status caused the university and its community to feel sensitivity towards the decrease of Jewish students. At the time many Jewish students at Princeton dated Jewish students at the University of Pennsylvania in Philadelphia because they perceived Princeton as an environment where it was difficult to find romantic prospects; Pam stated that there was a theory that the dating issues were a cause of the decline in Jewish students.
In 1981, the population of African Americans at Princeton University made up less than 10%. Bruce M. Wright was admitted into the university in 1936 as the first African American, however, his admission was a mistake and when he got to campus he was asked to leave. Three years later Wright asked the dean for an explanation on his dismissal and the dean suggested to him that “a member of your race might feel very much alone” at Princeton University.
Traditions
Princeton enjoys a wide variety of campus traditions, some of which, like the Clapper Theft and Nude Olympics, have faded into history:
Arch Sings – Late-night concerts that feature one or several of Princeton’s undergraduate a cappella groups, such as the Princeton Nassoons; Princeton Tigertones; Princeton Footnotes; Princeton Roaring 20; and The Princeton Wildcats. The free concerts take place in one of the larger arches on campus. Most are held in Blair Arch or Class of 1879 Arch.
Bonfire – Ceremonial bonfire that takes place in Cannon Green behind Nassau Hall. It is held only if Princeton beats both Harvard University and Yale University at football in the same season. The most recent bonfire was lighted on November 18, 2018.
Bicker – Selection process for new members that is employed by selective eating clubs. Prospective members, or bickerees, are required to perform a variety of activities at the request of current members.
Cane Spree – An athletic competition between freshmen and sophomores that is held in the fall. The event centers on cane wrestling, where a freshman and a sophomore will grapple for control of a cane. This commemorates a time in the 1870s when sophomores, angry with the freshmen who strutted around with fancy canes, stole all of the canes from the freshmen, hitting them with their own canes in the process.
The Clapper or Clapper Theft – The act of climbing to the top of Nassau Hall to steal the bell clapper, which rings to signal the start of classes on the first day of the school year. For safety reasons, the clapper has been removed permanently.
Class Jackets (Beer Jackets) – Each graduating class designs a Class Jacket that features its class year. The artwork is almost invariably dominated by the school colors and tiger motifs.
Communiversity – An annual street fair with performances, arts and crafts, and other activities that attempts to foster interaction between the university community and the residents of Princeton.
Dean’s Date – The Tuesday at the end of each semester when all written work is due. This day signals the end of reading period and the beginning of final examinations. Traditionally, undergraduates gather outside McCosh Hall before the 5:00 PM deadline to cheer on fellow students who have left their work to the very last minute.
FitzRandolph Gates – At the end of Princeton’s graduation ceremony, the new graduates process out through the main gate of the university as a symbol of the fact that they are leaving college. According to tradition, anyone who exits campus through the FitzRandolph Gates before his or her own graduation date will not graduate.
Holder Howl – The midnight before Dean’s Date, students from Holder Hall and elsewhere gather in the Holder courtyard and take part in a minute-long, communal primal scream to vent frustration from studying with impromptu, late night noise making.
Houseparties – Formal parties that are held simultaneously by all of the eating clubs at the end of the spring term.
Ivy stones – Class memorial stones placed on the exterior walls of academic buildings around the campus.
Lawnparties – Parties that feature live bands that are held simultaneously by all of the eating clubs at the start of classes and at the conclusion of the academic year.
Princeton Locomotive – Traditional cheer in use since the 1890s. It is commonly heard at Opening Exercises in the fall as alumni and current students welcome the freshman class, as well as the P-rade in the spring at Princeton Reunions. The cheer starts slowly and picks up speed, and includes the sounds heard at a fireworks show.
Or if a class is being celebrated, the last line consists of the class year repeated three times, e.g. “Eighty-eight! Eighty-eight! Eighty-eight!”
Newman’s Day – Students attempt to drink 24 beers in the 24 hours of April 24. According to The New York Times, “the day got its name from an apocryphal quote attributed to Paul Newman: ’24 beers in a case, 24 hours in a day. Coincidence? I think not.'” Newman had spoken out against the tradition, however.
Nude Olympics – Annual nude and partially nude frolic in Holder Courtyard that takes place during the first snow of the winter. Started in the early 1970s, the Nude Olympics went co-educational in 1979 and gained much notoriety with the American press. For safety reasons, the administration banned the Olympics in 2000 to the chagrin of students.
Prospect 11 – The act of drinking a beer at all 11 eating clubs in a single night.
P-rade – Traditional parade of alumni and their families. They process through campus by class year during Reunions.
Reunions – Massive annual gathering of alumni held the weekend before graduation.
Athletics
Princeton supports organized athletics at three levels: varsity intercollegiate, club intercollegiate, and intramural. It also provides “a variety of physical education and recreational programs” for members of the Princeton community. According to the athletics program’s mission statement, Princeton aims for its students who participate in athletics to be “‘student athletes’ in the fullest sense of the phrase. Most undergraduates participate in athletics at some level.
Princeton’s colors are orange and black. The school’s athletes are known as Tigers, and the mascot is a tiger. The Princeton administration considered naming the mascot in 2007, but the effort was dropped in the face of alumni opposition.
Varsity
Princeton is an NCAA Division I school. Its athletic conference is the Ivy League. Princeton hosts 38 men’s and women’s varsity sports. The largest varsity sport is rowing, with almost 150 athletes.
Princeton’s football team has a long and storied history. Princeton played against Rutgers University in the first intercollegiate football game in the U.S. on Nov 6, 1869. By a score of 6–4, Rutgers won the game, which was played by rules similar to modern rugby. Today Princeton is a member of the Football Championship Subdivision of NCAA Division I. As of the end of the 2010 season, Princeton had won 26 national football championships, more than any other school.
Club and intramural
In addition to varsity sports, Princeton hosts about 35 club sports teams. Princeton’s rugby team is organized as a club sport. Princeton’s sailing team is also a club sport, though it competes at the varsity level in the MAISA conference of the Inter-Collegiate Sailing Association.
Each year, nearly 300 teams participate in intramural sports at Princeton. Intramurals are open to members of Princeton’s faculty, staff, and students, though a team representing a residential college or eating club must consist only of members of that college or club. Several leagues with differing levels of competitiveness are available.
Songs
Notable among a number of songs commonly played and sung at various events such as commencement, convocation, and athletic games is Princeton Cannon Song, the Princeton University fight song.
Bob Dylan wrote Day of The Locusts (for his 1970 album New Morning) about his experience of receiving an honorary doctorate from the University. It is a reference to the negative experience he had and it mentions the Brood X cicada infestation Princeton experienced that June 1970.
“Old Nassau”
Old Nassau has been Princeton University’s anthem since 1859. Its words were written that year by a freshman, Harlan Page Peck, and published in the March issue of the Nassau Literary Review (the oldest student publication at Princeton and also the second oldest undergraduate literary magazine in the country). The words and music appeared together for the first time in Songs of Old Nassau, published in April 1859. Before the Langlotz tune was written, the song was sung to Auld Lang Syne’s melody, which also fits.
However, Old Nassau does not only refer to the university’s anthem. It can also refer to Nassau Hall, the building that was built in 1756 and named after William III of the House of Orange-Nassau. When built, it was the largest college building in North America. It served briefly as the capitol of the United States when the Continental Congress convened there in the summer of 1783. By metonymy, the term can refer to the university as a whole. Finally, it can also refer to a chemical reaction that is dubbed “Old Nassau reaction” because the solution turns orange and then black.
A quest for the origin of the most-distant quasars in the early universe.
Yuexing Li, associate professor of astronomy and astrophysics at Penn State. Credit: Yuexing Li. All Rights Reserved.
Astrophysicist Yuexing Li’s quest began with quasars, luminous galaxies powered by supermassive black holes actively devouring matter and releasing enormous amounts of electromagnetic radiation so hot and bright we can see it more than 13 billion light years away.
These colossal objects, formed less than a billion years after the Big Bang during a period called the Cosmic Dawn, have fascinated Li since she was a postdoc at Harvard University (US), where she was on the team that first modeled the formation of what was then the most distant known quasar.
“The most puzzling thing about these distant quasars” she said “is how did the supermassive black holes at their hearts form? Because they’re thought to weigh more than a billion suns, these black holes’ existence so early in the universe is difficult for us to explain with our theoretical models.”
The best-understood way black holes form is by the gravitational collapse of massive dying stars, which produces so-called stellar-mass black holes, with masses less than 100 times that of our sun.
These black holes may grow more massive by merging with other black holes and through a process called accretion, where surrounding matter is drawn into the black hole by its intense gravitational pull.
So could stellar-mass black holes formed by the deaths of the first stars have grown into the supermassive black holes powering those distant quasars?
Not according to recent cosmological simulations by Li and others, which point to black-hole seeds tens of thousands of times more massive.
“The consensus,” she said, “was that it’s extremely difficult, if not impossible, for those small seeds from the first stars to grow that big in that time — ten-millionfold within just a few hundred million years. But if such massive seeds were required, how could they possibly have formed?”
Critical conditions
In cosmological simulations, there’s an inherent trade-off between resolution (fineness of detail) and scale (relative size), and Li — now an associate professor of astronomy and astrophysics at Penn State — believes that trade-off may be the crux of the problem.
“A major problem with previous studies is that macroscale cosmological simulations do not have sufficient resolution to resolve the critical microscale physics of black hole growth,” she explained.
So Li developed a novel solution — combining large-scale simulations with small-scale simulations of ultrahigh resolution that would allow her to better model the formation and growth of small black holes in the early universe.
“With the unprecedented resolution of these new simulations,” she said, “I realized that some conclusions from previous papers may be only part of the story.”
Li had found the critical conditions under which those small black holes’ rate of accretion could exceed the standard limit, accelerating to what’s called super-Eddington accretion.
After inputting those conditions in her large-scale simulation, she knew she had found a solution.
“Indeed,” she said, “some of the small black holes were able to grow to a billion solar masses within a few hundred million years.”
A new frontier
Using her model — and another piece of cutting-edge code she developed, called ART2 — Li recently began a new study to discover the origin of the supermassive black holes powering the most-distant quasars.
With ART2 running on Penn State’s ROAR supercomputer, she can use her simulations to determine the likely observational properties of those first quasars, which she can then compare with existing data to make predictions for next-generation instruments like the James Webb Space Telescope (JWST).
The Pennsylvania State University (US) ROAR Supercomputer.
“This is a very important step to bridge the gap between simulation and observation,” she explained.
Using ART2, Li predicts that JWST, launched in December 2021, will be able to detect galaxies less than 300 million years after the Big Bang — pushing the cosmic frontier to an earlier epoch than ever before.
But even JWST, NASA’s most ambitious telescope, won’t be able to see electromagnetic radiation from small black holes at the Cosmic Dawn.
So Li is collaborating with Penn State’s LIGO group, studying gravitational waves — ripples in space-time — produced when black holes collide and merge.
“When those small black holes merge,” she explained, “the resulting gravitational waves, whose frequencies fall outside of the detection range of current ground-based observatories like LIGO, will be detectable by future observatories like LISA, the space-based gravitational-wave detector.”
That could enable follow-up observations in the electromagnetic spectrum and reveal an unprecedented level of detail about these mysterious objects.
“It’s like a window opening to a new world — a better understanding of how these structures formed — which will help us to understand how the universe has evolved,” Li said. “That is one of the unsolved puzzles of the early universe and, to me, one of the most exciting.”
The Pennsylvania State University (US) is a public state-related land-grant research university with campuses and facilities throughout Pennsylvania. Founded in 1855 as the Farmers’ High School of Pennsylvania, Penn State became the state’s only land-grant university in 1863. Today, Penn State is a major research university which conducts teaching, research, and public service. Its instructional mission includes undergraduate, graduate, professional and continuing education offered through resident instruction and online delivery. In addition to its land-grant designation, it also participates in the sea-grant, space-grant, and sun-grant research consortia; it is one of only four such universities (along with Cornell University(US), Oregon State University(US), and University of Hawaiʻi at Mānoa(US)). Its University Park campus, which is the largest and serves as the administrative hub, lies within the Borough of State College and College Township. It has two law schools: Penn State Law, on the school’s University Park campus, and Dickinson Law, in Carlisle. The College of Medicine is in Hershey. Penn State is one university that is geographically distributed throughout Pennsylvania. There are 19 commonwealth campuses and 5 special mission campuses located across the state. The University Park campus has been labeled one of the “Public Ivies,” a publicly funded university considered as providing a quality of education comparable to those of the Ivy League.
Annual enrollment at the University Park campus totals more than 46,800 graduate and undergraduate students, making it one of the largest universities in the United States. It has the world’s largest dues-paying alumni association. The university offers more than 160 majors among all its campuses.
Annually, the university hosts the Penn State IFC/Panhellenic Dance Marathon (THON), which is the world’s largest student-run philanthropy. This event is held at the Bryce Jordan Center on the University Park campus. The university’s athletics teams compete in Division I of the NCAA and are collectively known as the Penn State Nittany Lions, competing in the Big Ten Conference for most sports. Penn State students, alumni, faculty and coaches have received a total of 54 Olympic medals.
Early years
The school was sponsored by the Pennsylvania State Agricultural Society and founded as a degree-granting institution on February 22, 1855, by Pennsylvania’s state legislature as the Farmers’ High School of Pennsylvania. The use of “college” or “university” was avoided because of local prejudice against such institutions as being impractical in their courses of study. Centre County, Pennsylvania, became the home of the new school when James Irvin of Bellefonte, Pennsylvania, donated 200 acres (0.8 km2) of land – the first of 10,101 acres (41 km^2) the school would eventually acquire. In 1862, the school’s name was changed to the Agricultural College of Pennsylvania, and with the passage of the Morrill Land-Grant Acts, Pennsylvania selected the school in 1863 to be the state’s sole land-grant college. The school’s name changed to the Pennsylvania State College in 1874; enrollment fell to 64 undergraduates the following year as the school tried to balance purely agricultural studies with a more classic education.
George W. Atherton became president of the school in 1882, and broadened the curriculum. Shortly after he introduced engineering studies, Penn State became one of the ten largest engineering schools in the nation. Atherton also expanded the liberal arts and agriculture programs, for which the school began receiving regular appropriations from the state in 1887. A major road in State College has been named in Atherton’s honor. Additionally, Penn State’s Atherton Hall, a well-furnished and centrally located residence hall, is named not after George Atherton himself, but after his wife, Frances Washburn Atherton. His grave is in front of Schwab Auditorium near Old Main, marked by an engraved marble block in front of his statue.
Early 20th century
In the years that followed, Penn State grew significantly, becoming the state’s largest grantor of baccalaureate degrees and reaching an enrollment of 5,000 in 1936. Around that time, a system of commonwealth campuses was started by President Ralph Dorn Hetzel to provide an alternative for Depression-era students who were economically unable to leave home to attend college.
In 1953, President Milton S. Eisenhower, brother of then-U.S. President Dwight D. Eisenhower, sought and won permission to elevate the school to university status as The Pennsylvania State University. Under his successor Eric A. Walker (1956–1970), the university acquired hundreds of acres of surrounding land, and enrollment nearly tripled. In addition, in 1967, the Penn State Milton S. Hershey Medical Center, a college of medicine and hospital, was established in Hershey with a $50 million gift from the Hershey Trust Company.
Modern era
In the 1970s, the university became a state-related institution. As such, it now belongs to the Commonwealth System of Higher Education. In 1975, the lyrics in Penn State’s alma mater song were revised to be gender-neutral in honor of International Women’s Year; the revised lyrics were taken from the posthumously-published autobiography of the writer of the original lyrics, Fred Lewis Pattee, and Professor Patricia Farrell acted as a spokesperson for those who wanted the change.
In 1989, the Pennsylvania College of Technology in Williamsport joined ranks with the university, and in 2000, so did the Dickinson School of Law. The university is now the largest in Pennsylvania. To offset the lack of funding due to the limited growth in state appropriations to Penn State, the university has concentrated its efforts on philanthropy.
Research
Penn State is classified among “R1: Doctoral Universities – Very high research activity”. Over 10,000 students are enrolled in the university’s graduate school (including the law and medical schools), and over 70,000 degrees have been awarded since the school was founded in 1922.
Penn State’s research and development expenditure has been on the rise in recent years. For fiscal year 2013, according to institutional rankings of total research expenditures for science and engineering released by the National Science Foundation (US), Penn State stood second in the nation, behind only Johns Hopkins University (US) and tied with the Massachusetts Institute of Technology (US), in the number of fields in which it is ranked in the top ten. Overall, Penn State ranked 17th nationally in total research expenditures across the board. In 12 individual fields, however, the university achieved rankings in the top ten nationally. The fields and sub-fields in which Penn State ranked in the top ten are materials (1st), psychology (2nd), mechanical engineering (3rd), sociology (3rd), electrical engineering (4th), total engineering (5th), aerospace engineering (8th), computer science (8th), agricultural sciences (8th), civil engineering (9th), atmospheric sciences (9th), and earth sciences (9th). Moreover, in eleven of these fields, the university has repeated top-ten status every year since at least 2008. For fiscal year 2011, the National Science Foundation reported that Penn State had spent $794.846 million on R&D and ranked 15th among U.S. universities and colleges in R&D spending.
For the 2008–2009 fiscal year, Penn State was ranked ninth among U.S. universities by the National Science Foundation, with $753 million in research and development spending for science and engineering. During the 2015–2016 fiscal year, Penn State received $836 million in research expenditures.
The Applied Research Lab (ARL), located near the University Park campus, has been a research partner with the Department of Defense (US) since 1945 and conducts research primarily in support of the United States Navy. It is the largest component of Penn State’s research efforts statewide, with over 1,000 researchers and other staff members.
The Materials Research Institute was created to coordinate the highly diverse and growing materials activities across Penn State’s University Park campus. With more than 200 faculty in 15 departments, 4 colleges, and 2 Department of Defense research laboratories, MRI was designed to break down the academic walls that traditionally divide disciplines and enable faculty to collaborate across departmental and even college boundaries. MRI has become a model for this interdisciplinary approach to research, both within and outside the university. Dr. Richard E. Tressler was an international leader in the development of high-temperature materials. He pioneered high-temperature fiber testing and use, advanced instrumentation and test methodologies for thermostructural materials, and design and performance verification of ceramics and composites in high-temperature aerospace, industrial, and energy applications. He was founding director of the Center for Advanced Materials (CAM), which supported many faculty and students from the College of Earth and Mineral Science, the Eberly College of Science, the College of Engineering, the Materials Research Laboratory and the Applied Research Laboratories at Penn State on high-temperature materials. His vision for Interdisciplinary research played a key role in creating the Materials Research Institute, and the establishment of Penn State as an acknowledged leader among major universities in materials education and research.
The university was one of the founding members of the Worldwide Universities Network (WUN), a partnership that includes 17 research-led universities in the United States, Asia, and Europe. The network provides funding, facilitates collaboration between universities, and coordinates exchanges of faculty members and graduate students among institutions. Former Penn State president Graham Spanier is a former vice-chair of the WUN.
The Pennsylvania State University Libraries were ranked 14th among research libraries in North America in the 2003–2004 survey released by The Chronicle of Higher Education. The university’s library system began with a 1,500-book library in Old Main. In 2009, its holdings had grown to 5.2 million volumes, in addition to 500,000 maps, five million microforms, and 180,000 films and videos.
The university’s College of Information Sciences and Technology is the home of CiteSeerX, an open-access repository and search engine for scholarly publications. The university is also the host to the Radiation Science & Engineering Center, which houses the oldest operating university research reactor. Additionally, University Park houses the Graduate Program in Acoustics, the only freestanding acoustics program in the United States. The university also houses the Center for Medieval Studies, a program that was founded to research and study the European Middle Ages, and the Center for the Study of Higher Education (CSHE), one of the first centers established to research postsecondary education.
The “area law” says that a black hole’s surface area cannot decrease over time.
Gravitational waves from two merging black holes (shown in a simulation), spotted in 2015, revealed that the total surface area of the black holes doesn’t decrease when they merge. Credit: Simulating Extreme Spacetimes project.
Despite their mysterious nature, black holes are thought to follow certain simple rules. Now, one of the most famous black hole laws, predicted by physicist Stephen Hawking, has been confirmed with gravitational waves.
According to the black hole area theorem, developed by Hawking in the early 1970s, black holes can’t decrease in surface area over time. The area theorem fascinates physicists because it mirrors a well-known physics rule that disorder, or entropy, can’t decrease over time. Instead, entropy consistently increases (SN: 7/10/15).
That’s “an exciting hint that black hole areas are something fundamental and important,” says astrophysicist Will Farr of Stony Brook University (US) in New York and the Flatiron Institute (US) in New York City.
The surface area of a lone black hole won’t change — after all, nothing can escape from within. However, if you throw something into a black hole, it will gain more mass, increasing its surface area. But the incoming object could also make the black hole spin, which decreases the surface area. The area law says that the increase in surface area due to additional mass will always outweigh the decrease in surface area due to added spin.
To test this area rule, Massachusetts Institute of Technology (US) astrophysicist Maximiliano Isi, Farr and others used ripples in spacetime stirred up by two black holes that spiraled inward and merged into one bigger black hole. A black hole’s surface area is defined by its event horizon — the boundary from within which it’s impossible to escape. According to the area theorem, the area of the newly formed black hole’s event horizon should be at least as big as the areas of the event horizons of the two original black holes combined.
The team analyzed data from the first gravitational waves ever spotted, which were detected by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, in 2015 (SN: 2/11/16).
SWEET SUCCESS For the first time, physicists have directly observed gravitational waves, caused by two black holes colliding (illustrated here). Credit:SXS – Simulating eXtreme Spacetimes (US).
The researchers split the gravitational wave data into two time segments, before and after the merger, and calculated the surface areas of the black holes in each period. The surface area of the newly formed black hole was greater than that of the two initial black holes combined, upholding the area law with a 95 percent confidence level, the team reports in a paper to appear in Physical Review Letters.
“It’s the first time that we can put a number on this,” Isi says.
The area theorem is a result of the general theory of relativity, which describes the physics of black holes and gravitational waves. Previous analyses of gravitational waves have agreed with predictions of general relativity, and thus already hinted that the area law can’t be wildly off. But the new study “is a more explicit confirmation,” of the area law, says physicist Cecilia Chirenti of the University of Maryland (US) in College Park, who was not involved with the research.
So far, general relativity describes black holes well. But scientists don’t fully understand what happens where general relativity — which typically applies to large objects like black holes — meets quantum mechanics, which describes small stuff like atoms and subatomic particles. In that quantum realm, strange things can happen.
For example, black holes can release a faint mist of particles called Hawking radiation, another idea developed by Hawking in the 1970s. That effect could allow black holes to shrink, violating the area law, but only over extremely long periods of time, so it wouldn’t have affected the relatively quick merger of black holes that LIGO saw.
Physicists are looking for an improved theory that will combine the two disciplines into one new, improved theory of quantum gravity. Any failure of black holes to abide by the rules of general relativity could point physicists in the right direction to find that new theory.
So physicists tend to be grumpy about the enduring success of general relativity, Farr says. “We’re like, ‘aw, it was right again.’”
Just 5 years ago, physicists opened a new window on the universe when they first detected gravitational waves, ripples in space itself set off when massive black holes or neutron stars collide. Even as discoveries pour in, researchers are already planning bigger, more sensitive detectors. And a Ford versus Ferrari kind of rivalry has emerged, with scientists in the United States simply proposing bigger detectors, and researchers in Europe pursuing a more radical design.
“Right now, we’re only catching the rarest, loudest events, but there’s a whole lot more, murmuring through the universe,” says Jocelyn Read, an astrophysicist at California State University, Fullerton(US), who’s working on the U.S. effort. Physicists hope to have the new detectors running in the 2030s, which means they have to start planning now, says David Reitze, a physicist at the California Institute of Technology(US). “Gravitational wave discoveries have captivated the world, so now is a great time to be thinking about what comes next.”
Current detectors are all L-shaped instruments called interferometers. Laser light bounces between mirrors suspended at either end of each arm, and some of it leaks through to meet at the crook of the L. There, the light interferes in a way that depends on the arms’ relative lengths. By monitoring that interference, physicists can spot a passing gravitational wave, which will generally make the lengths of the arms waver by different amounts.
To tamp down other vibrations, the interferometer must be housed in a vacuum chamber and the weighty mirrors hung from sophisticated suspension systems. And to detect the tiny stretching of space, the interferometer arms must be long. In the Laser Interferometer Gravitational-Wave Observatory (LIGO), twin instruments in Louisiana and Washington state that spotted the first gravitational wave from two black holes whirling into each other, the arms are 4 kilometers long. Europe’s Virgo detector in Italy has 3-kilometer-long arms.
In spite of the detectors’ sizes, a gravitational wave changes the relative lengths of their arms by less than the width of a proton.
The dozens of black hole mergers that LIGO and Virgo have spotted have shown that stellar-mass black holes, created when massive stars collapse to points, are more varied in mass than theorists expected.
Masses in the Stellar Graveyard GWTC-2 plot v1.0 BY LIGO-Virgo. Credit: Frank Elavsky and Aaron Geller at Northwestern University(US).
In 2017, LIGO and Virgo delivered another revelation, detecting two neutron stars spiraling together and alerting astronomers to the merger’s location on the sky. Within hours telescopes of all types had studied the aftermath of the resulting “kilonova,” observing how the explosion forged copious heavy elements.
Researchers now want a detector 10 times more sensitive, which they say would have mind-boggling potential. It could spot all black hole mergers within the observable universe and even peer back to the time before the first stars to search for primordial black holes that formed in the big bang. It should also spot hundreds of kilonovae, laying bare the nature of the ultradense matter in neutron stars.
The U.S. vision for such a dream machine is simple. “We’re just going to make it really, really big,” says Read, who is helping design Cosmic Explorer, an interferometer with arms 40 kilometers long—essentially, a LIGO detector scaled up 10-fold.
The “cookie cutter design” might enable the United States to afford multiple, widely separated detectors, which would help pinpoint sources on the sky as LIGO and Virgo do now, says Barry Barish, a physicist at Caltech who directed the construction of LIGO.
Siting such mammoth wave catchers may be tricky. The 40-kilometer arms have to be straight, but Earth is round. If the crook of the L sits on the ground, then the ends of the interferometers might have to rest on berms 30 meters high. So U.S. researchers hope to find bowl-like areas that might accommodate the structure more naturally.
In contrast, European physicists envision a single subterranean gravitational wave observatory, called the Einstein Telescope [above], that would do it all. “We want to realize an infrastructure that is able to host all the evolutions [of detectors] for 50 years,” says Michele Punturo, a physicist with Italy’s National Institute for Nuclear Physics(IT) in Perugia and co-chair of the ET steering committee.
The ET would comprise multiple V-shaped interferometers with arms 10 kilometers long, arranged in an equilateral triangle deep underground to help shield out vibrations. With interferometers pointed in three directions, the ET could determine the polarization of gravitational waves—the direction in which they stretch space—to help locate sources on the sky and probe the fundamental nature of the waves.
The tunnels would actually house two sets of interferometers. The signals detected by LIGO and Virgo hum at frequencies that range from about 10 to 2000 cycles per second and rise as a pair of objects spirals together. But picking up lower frequencies of just a few cycles per second would open new realms. To detect them, a second interferometer that uses a lower power laser and mirrors cooled to near absolute zero would nestle in each corner of the ET. (Such mirrors are already in use at Japan’s KAGRA Large-scale Cryogenic Graviationai wave Telescope Project(JP) which has 3-kilometer arms and is striving to catch up with LIGO and Virgo.)
By going to lower frequencies, the ET could detect the merger of black holes hundreds of times as massive as the Sun. It could also catch neutron-star pairs hours before they actually merge, giving astronomers advance warning of kilonova explosions, says Marica Branchesi, an astronomer at Italy’s Gran Sasso Science Institute. “The early emission [of light] is extremely important, because there is a lot of physics there,” she says.
The ET should cost €1.7 billion, including €900 million for the tunneling and basic infrastructure, Punturo says. Researchers are considering two sites, one near where Belgium, Germany, and the Netherlands meet and another on the island of Sardinia. The plan is under review by the European Strategy Forum on Research Infrastructures, which could put the ET on its to-do list this summer. “This is an important political step,” Punturo says, but not final approval for construction.
The U.S. proposal is less mature. Researchers want the National Science Foundation(US) to provide $65 million for design work so a decision on the billion-dollar machine can be made in the mid-2020s, Barish says. Physicists hope to have both Cosmic Explorer and the ET running in the mid-2030s, at the same time as the planned Laser Interferometer Space Antenna, a constellation of three spacecraft millions of kilometers apart that will sense gravitational waves of far lower frequencies from supermassive black holes in the centers of galaxies.
The push for new gravitational wave detectors isn’t necessarily a competition. “What we really want is to have ET and Cosmic Explorer and, ideally, even a third detector of similar sensitivity,” says Stefan Hild, a physicist at Maastricht University [Universiteit Maastricht](NL) who works on the ET. Reitze notes, however, that timing and cost could “push towards convergence and simplicity in designs.” Instead of a Ford and a Ferrari, perhaps physicists will end up building a few Audis.
Research Contacts:
Volodymyr Takhistov
Project Researcher / Kavli IPMU Fellow
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
volodymyr.takhistov@ipmu.jp
George M. Fuller
Distinguished Professor of Physics
Director of Center for Astrophysics and Space Sciences
Department of Physics, University of California, San Diego
Email: gfuller@physics.ucsd.edu
Alexander Kusenko
Professor of Physics and Astronomy
Department of Physics and Astronomy, University of California, Los Angeles,
Visiting Senior Scientist
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
kusenko@ucla.edu
Media contact:
John Amari
Press officer
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
press@ipmu.jp
Fig.1: [Left] A tiny primordial black hole being captured by a neutron star, subsequently devouring it and leaving a “transmuted” solar-mass black hole remnant behind. [Right] Expected mass distribution of “transmuted” solar-mass black holes following neutron stars formed as a result of a delayed or a rapid supernova. The LIGO GW190814 event with 2.6 solar-mass black hole candidate is also shown. Credit: Takhistov et. al.)
What is the origin of black holes and how is that question connected with another mystery-the nature of Dark Matter*? Dark matter comprises the majority of matter in the Universe but its nature remains unknown.
Multiple gravitational wave detections of merging black holes have been identified within the last few years by the Laser Interferometer Gravitational-Wave Observatory (LIGO) commemorated with the 2017 physics Nobel Prize to Kip Thorne; Barry Barish; and Rainer Weiss.
Left to right: Rainer Weiss, Barry Barish and Kip Thorne, who have been awarded the 2017 Nobel prize in physics. Credit: Molly Riley/AFP/Getty Images.
Artist’s by now iconic conception of two merging black holes similar to those detected by LIGO. Credit: Caltech/MIT aLigo/Aurore Simonnet/Sonoma State.
ESA/eLISA the future of gravitational wave research
A definitive confirmation of the existence of black holes was celebrated with the 2020 physics Nobel Prize awarded to Andrea Ghez; Reinhard Genzel; and Roger Penrose. Understanding the origin of black holes has thus emerged as a central issue in physics.
Roger Penrose, Reinhard Genzel and Andrea Ghez have won the the 2020 Nobel Prize for Physics. (Courtesy: IOP Publishing/Tushna Commissariat; CC-BY-SA H Garching; UCLA/Christopher Dibble)
Surprisingly, LIGO has recently observed a 2.6 solar-mass black hole candidate (event GW190814, reported in Astrophysical Journal Letters). Assuming this is a black hole, and not an unusually massive neutron star, where does it come from?
Solar-mass black holes are particularly intriguing, since they are not expected from conventional stellar evolution astrophysics. Such black holes might arise in the early Universe (primordial black holes) or be “transmuted” from existing neutron stars. Some black holes could have formed in the early universe long before the stars and galaxies formed. Such primordial black holes could make up some part or all of dark matter. If a neutron star captures a primordial black hole, the black hole consumes the neutron star from the inside, turning it into a solar-mass black hole. This process can produce a population of solar mass black holes, regardless of how small the primordial black holes are. Other forms of dark matter can accumulate inside a neutron star causing its eventual collapse into a solar-mass black hole.
A new study, published in Physical Review Letters, advances a decisive test to investigate the origin of solar-mass black holes. This work was led by the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Fellow Volodymyr Takhistov and the international team included George M. Fuller, Distinguished Professor of Physics and Director of the Center for Astrophysics and Space Science at the University of California, San Diego(US), as well as Alexander Kusenko, Professor of Physics and Astronomy at the University of California, Los Angeles(US) and a Kavli IPMU Visiting Senior Scientist.
As the study discusses (see Fig. 1), “transmuted” solar-mass black holes remaining from neutron stars being devoured by dark matter (either tiny primordial black holes or particle dark matter accumulation) should follow the mass-distribution of the original host neutron stars. Since the neutron star mass distribution is expected to peak around 1.5 solar masses, it is unlikely that heavier solar-mass black holes have originated from dark matter interacting with neutron stars. This suggests that such events as the candidate detected by LIGO, if they indeed constitute black holes, could be of primordial origin from the early Universe and thus drastically affect our understanding of astronomy. Future observations will use this test to investigate and identify the origin of black holes.
Previously (see Physical Review Letters ), the same international team of researchers also demonstrated that disruption of neutron stars by small primordial black holes can lead to a rich variety of observational signatures and can help us understand such long-standing astronomical puzzles as the origin of heavy elements (e.g. gold and uranium) and the 511 keV gamma-ray excess observed from the center of our Galaxy.
*Dark Matter Background Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, some 30 years later, did most of the work on Dark Matter. Fritz Zwicky from http:// palomarskies.blogspot.com. Coma cluster via NASA/ESA Hubble.
In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter. Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science). Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL). Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.
Kavli Institute for the Physics and Mathematics of the Universe (IPMU) [カブリ数物連携宇宙研](JP) at U Tokyo {東京大学;Tōkyō daigaku](JP) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.
The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.
In this composite image, X-rays from Chandra and XMM-Newton have been colored blue and optical data from the NOIRLab Cerro Tololo Inter-American Observatory in Chile are colored red and green. The pulsar known as SXP 1062, is the bright white source located on the right-hand side of the image in the middle of the diffuse blue emission inside a red shell. The diffuse X-rays and optical shell are both evidence of a supernova remnant surrounding the pulsar. The optical data also displays spectacular formations of gas and dust in a star-forming region on the left side of the image. Image Credit: NASA/CXC/Univ.of Potsdam/L. Oskinova et al.
NASA Chandra X-ray Space Telescope.ESA/XMM Newton X-ray telescope (EU).NOIRLab CTIO Cerro Tololo Inter-American Observatory, approximately 80 km to the East of La Serena, Chile, at an altitude of 2200 meters.
In a universe chock-full of bizarre objects neutron stars rank near the top of the list. Although merely the size of a city, pulsars still pack in about one-and-a-half times the mass of our entire Sun.
Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.
Neutron stars manage to pull off this feat because their extreme gravity crushes atoms so tightly that the atoms’ protons and electrons fuse together, forming a hyperdense object composed almost entirely of neutrons (hence the moniker). Even the origin of neutron stars is intense—they’re forged when colossal stars cataclysmically explode as supernovae and the dying monster star’s pure iron core collapses in on itself.
For reasons not well-understood, a subset of these neutron stars soldier on as even wilder objects dubbed pulsars. These are neutron stars that spin anywhere from once every few seconds to many hundreds of times per second, sending beams of radiation sweeping through the cosmos like hyper lighthouses.
Measuring the characteristics of those beams is one of the main ways researchers are keying in on how neutron stars and pulsars alike work, in turn helping probe the boundaries of fundamental physics.
“Pulsar emissions are the primary signature of neutron stars, and neutron stars represent the most extreme matter in the observable universe,” says Roger Romani, a professor of physics at Stanford University(US) and a member of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC).
Romani and colleagues are keenly interested in the dividing line between neutron stars and the only objects made of even denser material, namely stellar black holes. (And which are not part of the “observable” universe, seeing as they do not emit light.) Stellar black holes form the same way as neutron stars, when ginormous stars go boom, though in the former’s case, the leftover stellar cinder compacts so tightly that its gravity traps light, and the object goes “dark.”
The dividing line is one of mass, where the most massive stars yield the most massive cores that, at some threshold, generate the gravity necessary to progress past neutron-starhood and into black holiness. (Forgive the punnery.) Researchers want to better understand this boundary and reap the insights it will provide into how matter behaves in conditions completely unreplicable on Earth.
“I’ve been chasing down where the neutron star – black hole boundary is,” says Romani. “How massive can a neutron star get before it disappears, collapsing into a black hole?”
Pulsars are in fact paving the way to this understanding, specifically a kind of pulsar with the ominous nickname “black widow.” These are pulsars that steadily destroy companion stars with energetic outflows, oftentimes gravitationally slurping up some of the scattered matter from their victims. (The nickname derives from how female black widow spiders tend to eat their male partners, an act that gave the spiders their evocative appellation in the first place.) The rate of pulses from some black widow pulsars suggest they’ve have gobbled up so much matter that they’re at the “brink of collapse,” Romani says, and could transition into being black holes.
Other important insights into neutron star physics will come via gravitational wave astronomy. It’s a field that sprung to life just six years ago with the announcement of the first-ever direct detection of gravitational waves by the LIGO observatory (led in part by members of the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology).
Kavli MIT Institute For Astrophysics and Space Research. Caltech/MIT Advanced aLigo Hanford, WA, USA installation Caltech/MIT Advanced aLigo detector installation Livingston, LA, USACornell SXS, the Simulating eXtreme Spacetimes (SXS) project Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
ESA/eLISA the future of gravitational wave research
As LIGO and its ilk capture more events in the years ahead spawned by the energetic mergers of neutron stars, as well as black holes and neutron stars, astrophysicists will gain a vital new dataset. “Gravitational wave signatures can also help once we get a large sample of neutron star-containing mergers,” Romani says.
Also helpful will be pulsar pulses not of the usual radio-wave variety measured in abundance since the discovery of pulsars in 1967. “For the radio emission, we are flooded in data,” says Romani. “But most of it is ‘weather’ and it is hard to see how we will cut through this to probe the underlying physics.”
Instead, harder-to-corral, higher-energy light, such as gamma rays and x-rays, is now broadening our understanding of the mechanisms driving pulsars.
“For the extreme physics questions, additional measurements of neutron star masses, radii, and surface emissions, especially in the x-ray band, offer good hope of near-future progress,” says Romani.
The KIPAC researcher expects this wealth of data will help answer one of the biggest outstanding mystery about pulsars—how the heck do they generate their telltale radio pulses, anyway? “Some plausible models have been proposed,” Romani says. “But there is as yet no generally accepted picture.”
It goes to show that while neutron stars and pulsars are pushing astrophysics into new frontiers, some age-old, basic questions about these extraordinary objects still need answering.
The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.
The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.
The Kavli Foundation, based in Los Angeles, California, is a foundation that supports the advancement of science and the increase of public understanding and support for scientists and their work.
The Kavli Foundation was established in December 2000 by its founder and benefactor, Fred Kavli, a Norwegian business leader and philanthropist, who made his money by creating Kavlico, a company that made sensors, and by investing in real estate in southern California and Nevada. David Auston, a former president of Case Western Reserve University and former Bell Labs scientist, was the first president of the Kavli Foundation and is largely credited with the vision of the scientific investments. Kavli died in 2013, and his foundation is currently actively involved in establishing research institutes at universities throughout the United States, in Europe, and in Asia.
To date, the Kavli Foundation has made grants to establish Kavli Institutes on the campuses of 16 major universities. In addition to the Kavli Institutes, six Kavli professorships have been established: two at University of California, Santa Barbara, one each at University of California, Los Angeles, University of California, Irvine, Columbia University, Cornell University, and California Institute of Technology.
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Bethany Downer
ESA/Hubble Space Telescope
bethany.downer@esahubble.org
Science Contacts:
Eduardo Vitral
Institut d’Astrophysique de Paris (IAP)(FR)
vitral@iap.fr
Dr. Gary A. Mamon
Institut d’Astrophysique de Paris (IAP) (FR)
gam@iap.fr
Compass Image for NGC 6397
Credits: Image: NASA/ESA, T. Brown, S. Casertano, and J. Anderson (STScI) (US)
Science: NASA/ ESA E. Vitral and G. Mamon (Institut d’Astrophysique de Paris (IAP) (FR)
Summary
The idea that black holes come in different sizes may sound a little odd at first. After all, a black hole by definition is an object that has collapsed under gravity to an infinite density, making it smaller than the period at the end of this sentence. But the amount of mass a black hole can pack away varies widely from less than twice the mass of our Sun to over a billion times our Sun’s mass. Midway between are intermediate-mass black holes (IMBHs) weighing roughly hundreds to tens of thousands of solar masses. So, black holes come small, medium, and large.
However, the IMBHs have been elusive. They are predicted to hide out in the centers of globular star clusters, beehive-shaped swarms of as many as a million stars. Hubble researchers went hunting for an IMBH in the nearby globular cluster NGC 6397 and came up with a surprise. Because a black hole cannot be seen, they carefully studied the motion of stars inside the cluster, that would be gravitationally affected by the black hole’s gravitational tug. The amplitudes and shapes of the stellar orbits led to the conclusion that there is not just one hefty black hole, but a swarm of smaller black holes – a mini-cluster in the core of the globular.
Why are the black holes hanging out together? A gravitational pinball game takes place inside globular clusters where more massive objects sink to the center by exchanging momentum with smaller stars, that then migrate to the cluster’s periphery. The central black holes may eventually merge, sending ripples across space as gravitational waves.
Astronomers found something they weren’t expecting at the heart of the globular cluster NGC 6397: a concentration of smaller black holes lurking there instead of one massive black hole.
Globular clusters are extremely dense stellar systems, which host stars that are closely packed together. These systems are also typically very old — the globular cluster at the focus of this study, NGC 6397, is almost as old as the universe itself. This cluster resides 7,800 light-years away, making it one of the closest globular clusters to Earth. Due to its very dense nucleus, it is known as a core-collapsed cluster.
At first, astronomers thought the globular cluster hosted an intermediate-mass black hole (IMBH). These IMBHs are the long-sought “missing link” between supermassive black holes (many millions of times our Sun’s mass) that lie at the cores of galaxies, and stellar-mass black holes (a few times our Sun’s mass) that form following the collapse of a single massive star. Their mere existence is hotly debated. Only a few candidates have been identified to date.
“We found very strong evidence for an invisible mass in the dense core of the globular cluster, but we were surprised to find that this extra mass is not ‘point-like’ (that would be expected for a solitary massive black hole) but extended to a few percent of the size of the cluster,” said Eduardo Vitral of the Paris Institute of Astrophysics, (IAP) (FR).
To detect the elusive hidden mass, Vitral and Gary Mamon, also of IAP, used the velocities of stars in the cluster to determine the distribution of its total mass, that is the mass in the visible stars, as well as in faint stars and black holes. The more mass at some location, the faster the stars travel around it.
The researchers used previous estimates of the stars’ tiny proper motions (their apparent motions on the sky), which allow for determining their true velocities within the cluster. These precise measurements for stars in the cluster’s core could only be made with Hubble over several years of observation. The Hubble data were added to well-calibrated proper motion measurements provided by the European Space Agency’s Gaia space observatory, but which are less precise than Hubble’s observations in the core.
ESA (EU)/GAIA satellite .
“Our analysis indicated that the orbits of the stars are close to random throughout the globular cluster, rather than systematically circular or very elongated,” explained Mamon. These moderate-elongation orbital shapes constrain what the inner mass must be.
The researchers conclude that the invisible component can only be made of the remnants of massive stars (white dwarfs, neutron stars, and black holes) given its mass, extent and location. These stellar corpses progressively sank to the cluster’s center after gravitational interactions with nearby less massive stars. This game of stellar pinball is called “dynamical friction,” where, through an exchange of momentum, heavier stars are segregated in the cluster’s core and lower-mass stars migrate to the cluster’s periphery.
“We used the theory of stellar evolution to conclude that most of the extra mass we found was in the form of black holes,” said Mamon. Two other recent studies had also proposed that stellar remnants, in particular, stellar-mass black holes, could populate the inner regions of globular clusters. “Ours is the first study to provide both the mass and the extent of what appears to be a collection of mostly black holes in the center of a core-collapsed globular cluster,” added Vitral [Astronomy & Astrophysics].
The astronomers also note that this discovery raises the possibility that mergers of these tightly packed black holes in globular clusters may be an important source of gravitational waves, ripples through spacetime. Such phenomena could be detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) experiment. LIGO is funded by the National Science Foundation and operated by Caltech and MIT.
Three years ago, two neutron stars collided in a cataclysmic crash, the first such merger ever observed directly. Naturally, scientists kept their eye on it — and now, something strange is happening.
Astrophysicists observed the star collision on Aug. 17, 2017, spotting for the first time ever signs of the same event in both a gravitational-wave chirp detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) on Earth and a massive burst of different flavors of light.
MIT /Caltech Advanced aLigo .
The X-rays observed at the location 130 million light-years from Earth peaked less than six months after the merger’s discovery, then began to fade. But in observations gathered this year, that trend has stopped, and an X-ray signal is unexpectedly lingering, according to research presented on Thursday (Jan. 14) at the 237th meeting of the American Astronomical Society, held virtually due to the pandemic.
“Our models so far were describing the observation incredibly well, so we thought we nailed it down,” Eleonora Troja, an astrophysicist at the University of Maryland and NASA’s Goddard Space Flight Center in Maryland, told Space.com. “I think everybody was convinced that this thing was going to fade quickly, and the last observation showed that it is not.”
A star crash checkup … and mystery
When NASA’s Chandra X-ray Observatory checked in on the former merger in the spring, things were beginning to look fishy.
NASA Chandra X-ray Space Telescope.
Scientists thought they were looking at the afterglow of the high-energy jet of material shot out by the collision, and they had expected the X-rays to have faded by the spring. But the source was still glowing in the spacecraft’s view. When the telescope looked again, in December, it still found a bright X-ray signal.
It’s too early to know what precisely is happening, Troja said. Chandra may not look again until this December, although she plans to ask for the telescope to change plans to check in sooner. Radio instruments can study the collision more frequently, and could help solve the puzzle between now and then.
For now, Troja believes one of two hypotheses will explain the continued X-ray emissions.
In one scenario, the lingering X-rays are joined by radio light within the next eight months or year. Troja said that would suggest that scientists are seeing not the afterglow of jets shooting out from the collision, but the afterglow of the massive kilonova explosion itself — something scientists have never seen before.
An artist’s depiction of a cloud of debris created by a neutron-star collision. Credit: NASA’s Goddard Space Flight Center/CI Lab.
“People think that in the 21st century we have seen it all and there is no first time left,” she said. Not so if this hypothesis holds. “This would be a first, it would be a new type of light, a new form of astrophysical source that we have never seen before.”
If the X-ray emissions continue but no radio emissions join them, Troja thinks scientists may be looking at something perhaps still more intriguing: proof that the collision formed a massive neutron star, the most massive such object known to date.
Soon after the collision, scientists calculated the mass of the initial neutron stars and the mass of what was left, after the dramatics shot matter out into space. But that value is between the current largest known neutron star and the smallest known black hole, leaving scientists stumped. The new observations could decide it: If the object is emitting X-rays, it sure isn’t a black hole. Confirming the result of the collision would give scientists an opportunity to better understand how matter behaves in superdense neutron stars, she said.
“We have a beautiful problem,” Troja said. “No matter what the solution is, it’s going to be exciting, which is a great problem to have in astrophysics.”
Driven by the pursuit of excellence, the University of Maryland has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.
The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.
Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.
One of the biggest galaxies in the universe seems to lack its dark centerpiece.
The galaxy cluster Abell 2261, captured by the Hubble Space Telescope. The brightest galaxy, center left, is about one million light-years across and about 10 times the diameter of the Milky Way.Credit: NASA/ESA Hubble, M. Postman (STScI), T. Lauer (NOIRLab/NOAO), and the CLASH team.
Astronomers are searching the cosmic lost-and-found for one of the biggest, baddest black holes thought to exist. So far they haven’t found it.
In the past few decades, it has become part of astronomical lore, if not quite a law, that at the center of every luminous city of light, called a galaxy, lurks something like a hungry Beelzebub, a giant black hole into which the equivalent of millions or even billions of suns have disappeared. The bigger the galaxy, the more massive the black hole at its center.
So it was a surprise a decade ago when Marc Postman, of the Space Telescope Science Institute, using the Hubble Space Telescope to survey clusters of galaxies, found a supergiant galaxy [The Astrophysical Journal] with no sign of a black hole in its center. Normally, the galaxy’s core would have a kink of extra light in its center, a kind of sparkling cloak, produced by stars that had been gathered there by the gravity of a giant black hole.
On the contrary, at the exact center of the galaxy’s wide core, where a slight bump in starlight should have been, there was a slight dip. Moreover, the entire core, a cloud of stars some 20,000 light years across, was not even centered on the exact middle of the galaxy.
“Oh, my God, this is really unusual,” Tod Lauer, an expert on galactic nuclei at the NOIRLab National Optical Astronomy Observatory in Tucson, Ariz., and an author on the paper, recalled saying when Dr. Postman showed him the finding.
Kitt Peak NOIRLab National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft), annotated.
That was in 2012. In the years since, the two researchers and their colleagues have been ransacking the galaxy, looking for X-rays or radio waves from the missing black hole.
The galaxy is the brightest one in a cluster known as Abell 2261. It is about 2.7 billion light-years from here, in the constellation Hercules in the northern sky, not far from the prominent star Vega. Using the standard rule of thumb, the black hole missing from the center of the 2261 galaxy should be 10 billion solar masses or more, comparable to the mightiest of these monsters known to astronomers. The black hole at the center of the Milky Way galaxy is only about four million solar masses.
SGR A and SGR A* from Penn State and NASA/Chandra. SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory.
So where has nature stashed the equivalent of 10 billion suns?
One possibility is that the black hole is there but has gone silent, having temporarily run out of anything to eat. But another provocative possibility, Dr. Lauer and his colleagues say, is that the black hole was thrown out of the galaxy altogether.
‘A pit in every peach’
Proving the latter could provide insight into some of the most violent and dynamic processes in the evolution of galaxies and the cosmos, about which astronomers have theorized but never seen — a dance of titanic forces and swirling worlds that can fling stars and planets across the void.
“It’s an intriguing mystery, and we’re on the case,” Dr. Postman said in an email. He added that the upcoming James Webb Space Telescope would have the capability to shed light, so to speak, on the case.
“What happens when you eject a supermassive black hole from a galaxy?” Dr. Lauer asked.
“The story of A2261-BCG,” he said, referring to the galaxy’s formal name in literature, “is what happens with the most massive galaxies in the universe, the giant elliptical galaxies, at the end point of galaxy evolution.”
Dr. Lauer is part of an informal group who call themselves Nukers. The group, whose membership is fluid — “like a band,” he said — first came together under Sandra Faber of the University of California, Santa Cruz, in the early days of the Hubble Space Telescope. Over the past four decades, they have sought to elucidate the nature of galactic nuclei, using the sharp eye of Hubble and other new facilities to peer into the intimate hearts of distant galaxies.
Radio emissions detected near the center of the galaxy suggested supermassive black hole activity had taken place there 50 million years ago.Credit: NASA/CXC, NASA/STScI, NAOJ/Subaru, NSF/NRAO/VLA.
NASA Chandra X-ray Space Telescope.NASA/ESA Hubble Telescope.NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level.NRAO Karl G Jansky Very Large Array, located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.
Black holes are objects so dense that not even light can escape their gravitational clutches. They are invisible by definition, but the ruckus — X-rays and radio screams — caused by material falling into its grasp can be seen across the universe. The discovery in the 1960s of quasars in the centers of galaxies first led astronomers to consider that supermassive black holes were responsible for such fireworks.
By the turn of the century, astronomers had come to the conclusion that every galaxy harbored a supermassive black hole, millions to billions of times more massive than the sun, in its bosom. Where they came from — whether they grew from smaller black holes that had formed from the collapse of stars, or formed through some other process early in the universe — nobody is sure. “There is a pit in every peach,” Dr. Lauer said.
But how do these entities affect their surroundings?
In 1980, three astronomers, Mitchell Begelman, Martin Rees and Roger Blandford, wrote about how these black holes would alter the evolution of the galaxies they inhabit. When two galaxies collided and merged — an especially common event in the earlier universe — their central black holes would meet and form a binary system, two black holes circling each other.
Dr. Begelman and his colleagues argued that these two massive black holes, swinging around, would interact with the sea of stars they were immersed in. Every once in a while, one of these stars would have a close encounter with the binary, and gravitational forces would push the star out of the center, leaving the black holes even more tightly bound.
Over time, more and more stars would be tossed away from the center. Gradually, starlight that was once concentrated at the center would spread out into a broader, diffuse core, with a little kink at the center where the black-hole binary was doing its mating dance. The process is called “scouring.”
“They were way ahead of the game,” Dr. Lauer said of the three astronomers.
A knotty problem
A scoured core was the kind of situation that Dr. Lauer and Dr. Postman thought they had encountered with Abell 2261. But instead of a peak at the center of the core, there was a dip, as if the supermassive black hole and its attendant stars had simply been taken away.
This raised the even more dramatic possibility that the scenario envisioned by Dr. Begelman and his colleagues had played out all the way to the end: The two black holes had merged into one gigantic mouthful of nothing. The merger would have been accompanied by a cataclysmic burst of gravitational waves, space-time ripples predicted to exist by Einstein in 1916 and finally seen by the LIGO instruments a century later, in 2016.
Caltech/MIT Advanced aLigo Hanford, WA, USA installation Caltech/MIT Advanced aLigo detector installation Livingston, LA, USACornell SXS, the Simulating eXtreme Spacetimes (SXS) project Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
ESA/eLISA the future of gravitational wave research
If that burst was lopsided, it would have sent the resultant supermassive black hole flying through the galaxy, or even out of it, something astronomers had never observed. So finding the errant black hole was of the utmost importance.
Further scrutiny of A2261-BCG revealed four little knots of light within the diffuse core. Could one of them be harboring the black hole?
A team led by Sarah Burke-Spolaor of West Virginia University took to the sky with Hubble [above] and the Very Large Array [above] radio telescope in Socorro, New Mexico. Spectroscopic measurements by the Hubble could tell how fast the stars in the knots were jiggling around, and thus whether some massive object — a black hole — was needed to keep them all together.
Two of the knots, they concluded, were probably small galaxies with small internal motions being cannibalized by the big galaxy. Measurements of the third knot had such large error bars that it could not yet be ruled in or out as the black hole’s location.
The fourth, very compact knot near the bottom edge of the core was too faint even for the Hubble, Dr. Burke-Spoloar reported. “Observing this knot would have required an overblown amount of time (hundreds of hours) observing with Hubble Space Telescope,” she said in an email, and so it also remains a candidate for the black-hole hiding spot.
The galaxy core also emits radio waves, but they didn’t help the search, Dr. Burke-Spolaor said.
“We were originally hoping the radio emission would be some kind of literal smoking gun, showing an active jet that points directly back to black-hole location,” she said. But the radio relic was at least 50 million years old, according to its spectral characteristics, which meant, she said, that the large black hole would have had ample time to move elsewhere since the jet turned off.
Next stop was NASA’s orbiting Chandra X-ray Observatory [above]. Kayhan Gultekin of the University of Michigan, another veteran Nuker who was not on the original discovery team, aimed the telescope at the cluster core and those suspicious knots. No dice. The putative black hole would have to be feeding at one-millionth of its potential rate if it were there at all, Dr. Gultekin said.
“Either any black hole at the center is very faint, or it isn’t there,” he wrote in an email. The same goes for the case of a binary black-hole system, he said; it would need to be eating very little gas to stay hidden.
In the meantime, Imran Nasim, of the University of Surrey in the U.K., who was not part of Dr. Postman’s team, has published a detailed analysis [MNRAS] of how the merger of two supermassive black holes could reform the galaxy into what the astronomers have found.
“Simply, gravitational wave recoil ‘kicks’ the supermassive black hole out of the galaxy,” Dr. Nasim explained in an email. Having lost its supermassive anchor, the cloud of stars around the black hole binary spreads out, becoming more diffuse. The density of stars in that region — the densest part of the entire giant galaxy — is only one-tenth the density of stars in our own neighborhood of the Milky Way, resulting in a night sky that would appear anemic compared with our own.
All this is another reason that astronomers eagerly await the launch of the James Webb Space Telescope, the long-awaited successor to Hubble, which is now scheduled for the end of October. That telescope will be able to examine all four knots at the same time and determine whether any of them are a cloaked, supermassive black hole.
“Here you see our great sophistication,” Dr. Lauer said. “Hey! Maybe it’s in the knots! — Hey maybe it isn’t! Better search everything!”
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