From Harvard-Smithsonian Center for Astrophysics: “Comet or Asteroid- What Killed the Dinosaurs And Where Did it Come From?”

From Harvard-Smithsonian Center for Astrophysics

February 15, 2021

Nadia Whitehead
Public Affairs Officer
Center for Astrophysics | Harvard & Smithsonian
nadia.whitehead@cfa.harvard.edu
617-721-7371

An artist’s impression of what the Chicxulub crater might have looked like soon after an asteroid struck the Yucatán Peninsula in Mexico. Researchers studied the peak rings, or circular hills, inside the crater. Credit: Detlev van Ravenswaay/Science Source.

The Chicxulub impactor, as it’s known, left behind a crater off the coast of Mexico that spans 93 miles and runs 12 miles deep. Its devastating impact brought the reign of the dinosaurs to an abrupt and calamitous end by triggering their sudden mass extinction, along with the end of almost three-quarters of the plant and animal species living on Earth.

The enduring puzzle: Where did the asteroid or comet originate, and how did it come to strike Earth? Now, a pair of researchers at the Center for Astrophysics | Harvard & Smithsonian believe they have the answer.

In a study published today in Nature’s Scientific Reports, Harvard University astrophysics undergraduate student Amir Siraj and astronomer Avi Loeb put forth a new theory that could explain the origin and journey of this catastrophic object.

Using statistical analysis and gravitational simulations, Siraj and Loeb calculate that a significant fraction of long-period comets originating from the Oort cloud, an icy sphere of debris at the edge of the solar system, can be bumped off-course by Jupiter’s gravitational field during orbit.

Kuiper Belt and Oort Cloud. Credit: NASA.

“The solar system acts as a kind of pinball machine,” explains Siraj, who is pursuing bachelor’s and master’s degrees in astrophysics, in addition to a master’s degree in piano performance at the New England Conservatory of Music. “Jupiter, the most massive planet, kicks incoming long-period comets into orbits that bring them very close to the sun.”

During close passage to the sun, the comets — nicknamed “sungrazers” — can experience powerful tidal forces that break apart pieces of the rock and ultimately, produce cometary shrapnel.

“In a sungrazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object,” Siraj says. “You can get what’s called a tidal disruption event, in which a large comet breaks up into many smaller pieces. And crucially, on the journey back to the Oort cloud, there’s an enhanced probability that one of these fragments hit the Earth.”

The new calculations from Siraj and Loeb’s theory increase the chances of long-period comets impacting Earth by a factor of about 10, and show that about 20 percent of long-period comets become sungrazers.

The pair say that their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

“Our paper provides a basis for explaining the occurrence of this event,” Loeb says. “We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs.”

Evidence found at the Chicxulub crater suggests the rock was composed of carbonaceous chondrite. Siraj and Loeb’s hypothesis might also explain this unusual composition.

A popular theory on the origin of Chicxulub claims that the impactor originated from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. However, carbonaceous chondrites are rare amongst main-belt asteroids, but possibly widespread amongst long-period comets, providing additional support to the cometary impact hypothesis.

Other similar craters display the same composition. This includes an object that hit about 2 billion years ago and left the Vredefort crater in South Africa, which is the largest confirmed crater in Earth’s history, and the impactor that left the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years. The researchers say that the timing of these impacts support their calculations on the expected rate of Chicxulub-sized tidally disrupted comets.

Siraj and Loeb say their hypothesis can be tested by further studying these craters, others like them, and even ones on the surface of the moon to determine the composition of the impactors. Space missions sampling comets can also help.

Aside from composition of comets, the new Vera Rubin Observatory in Chile may be able to observe tidal disruption of long-period comets after it becomes operational next year.

NOIRLab Vera C. Rubin Observatory Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,715 m (8,907 ft).

“We should see smaller fragments coming to Earth more frequently from the Oort cloud,” Loeb says. “I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments.”

Loeb says understanding this is not just crucial to solving a mystery of Earth’s history but could prove pivotal if such an event were to threaten the planet.

“It must have been an amazing sight, but we don’t want to see that again,” he said.

See the full article here.

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Modeling Galaxy Formation”

From Harvard-Smithsonian Center for Astrophysics

An image of a computer-simulated Milky Way-like galaxy. Astronomers have added improvements to previous codes so that they now can more accurately include processes involving dust, molecular hydorgen, and feedback from radiation on star formation, marking a significant advance in galaxy evolution modeling.
Credit: Kannan et al. 2020.

Understanding the formation and evolution of galaxies is difficult because so many different physical processes besides just gravity are involved, including processes associated with star formation and stellar radiation, the cooling of the gas in the interstellar medium, feedback from accreting black holes, magnetic fields, cosmic rays, and more. Astronomers have used computer simulations of galaxy formation to help understand the interplay of these processes and address questions that cannot yet be answered through observations, like how the first galaxies in the universe formed.

The simulations were performed on the Pleiades Supercomputer located at NASA Advanced Supercomputing (NAS) facility at the Ames Research Center.

NASA SGI Intel Advanced Supercomputing Center Pleiades Supercomputer, housed at the NASA Advanced Supercomputing (NAS) facility at NASA’s Ames Research Center.

Simulations of galaxy formation require the self-consistent modelling of all these various mechanisms at once, but a key difficulty is that each of them operates at a different spatial scale making it nearly impossible to properly simulate them all at the same time. Gas inflow from the intergalactic medium into a galaxy, for example, takes place across millions of light-years, the winds of stars have influence over hundreds of light-years, while black hole feedback from its accretion disc occurs at scales of thousandths of a light-year.

CfA astronomers Rahul Kannan and Lars Hernquist, with their colleagues, have developed a novel computational framework that self-consistently includes all these effects. The computations use a new stellar feedback framework called the Stars and Multiphase Gas in Galaxies (SMUGGLE) which integrates processes involving radiation, dust, molecular hydrogen gas (the dominant component of the interstellar medium) and also includes thermal and chemical modeling. The SMUGGLE feedback is incorporated into the popular AREPO hydrodynamic code that simulates the evolution of structures, and which has an added module to include radiation effects.

The astronomers use a simulation of the Milky Way to test their results, and report very good agreement with observations. They find that the feedback effects from radiation on star formation rates are quite modest, at least in a Milky Way example, where stars are forming at a rate of only two-to-three solar-masses per year. On the other hand, they find that the radiation from stars drastically changes the structure and heating of the interstellar medium by influencing the distribution of the hot, warm, and cold material which diverges from the simple expectation. The code does a good job of simulating the dust temperature distribution with warm dust lying (as expected) near the star-forming regions but with the cold dust, perhaps as low as ten kelvin, distributed farther away. The success of these new simulations motivates the authors to extend their work to simulations at even finer spatial resolution.

Science paper:
Simulating the Interstellar Medium of Galaxies with Radiative Transfer, Non-equilibrium Thermochemistry, and Dust
MNRAS

See the full article here .

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Please help promote STEM in your local schools.

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “High Schoolers Discover Four Exoplanets Through Harvard & Smithsonian Mentorship Program”

From Harvard-Smithsonian Center for Astrophysics

An artist’s rendering of a five-planet system around TOI-1233 includes a super-Earth (foreground) that could help solve mysteries of planet formation. The four innermost planets were discovered by high schoolers Kartik Pinglé and Jasmine Wright alongside researcher Tansu Daylan. The fifth outermost planet pictured was recently discovered by a separate team of astronomers. Credit: NASA/JPL-Caltech.

This week, 16-year-old Kartik Pinglé and 18-year-old Jasmine Wright have co-authored a peer-reviewed paper in The Astronomical Journal describing the discovery of four new exoplanets about 200-light-years away from Earth.

The high schoolers participated in the research through the Student Research Mentoring Program (SRMP) at the Center for Astrophysics | Harvard & Smithsonian. Directed by astrochemist Clara Sousa-Silva, the SRMP connects local high schoolers who are interested in research with real-world scientists at Harvard and MIT. The students then work with their mentors on a year-long research project.

“It’s a steep learning curve,” says Sousa-Silva, but it’s worth it. “By the end of the program, the students can say they’ve done active, state-of-the-art research in astrophysics.”

Pinglé and Wright’s particular achievement is rare. High schoolers seldom publish research, Sousa-Silva says. “Although that is one of the goals of the SRMP, it is highly unusual for high-schoolers to be co-authors on journal papers.”

With guidance from mentor Tansu Daylan, a postdoc at the MIT Kavli Institute for Astrophysics and Space Research, the students studied and analyzed data from the Transiting Exoplanet Survey Satellite (TESS). TESS is a space-based satellite that orbits around Earth and surveys nearby bright stars with the ultimate goal of discovering new planets.

NASA/MIT Tess

NASA/MIT Tess in the building.

NASA/MIT TESS replaced Kepler in search for exoplanets.

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA’s Goddard Space Flight Center.

Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames Research Center in California’s Silicon Valley; the Center for Astrophysics – Harvard and Smithsonian in Cambridge; MIT Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore.

The team focused on TESS Object of Interest (TOI) 1233, a nearby, bright Sun-like star. To perceive if planets were rotating around the star, they narrowed in on TOI-1233’s light.

“We were looking to see changes in light over time,” Pinglé explains. “The idea being that if the planet transits the star, or passes in front of it, it would [periodically] cover up the star and decrease its brightness.”

Planet transit. NASA/Ames.

To the team’s surprise, they discovered not one but four planets rotating around TOI-1233.

“I was very excited and very shocked,” Wright says. “We knew this was the goal of Daylan’s research, but to actually find a multiplanetary system, and be part of the discovering team, was really cool.”

Three of the planets are considered “sub-Neptunes,” gaseous planets that are smaller than, but similar to our own solar system’s Neptune. It takes between 6 and 19.5 days for each of them to orbit around TOI-1233. The fourth planet is labeled a “super-Earth” for its large size and rockiness; it orbits around the star in just under four days.

Daylan hopes to study the planets even closer in the coming year.

“Our species has long been contemplating planets beyond our solar system and with multi-planetary systems, you’re kind of hitting the jackpot,” he says. “The planets originated from the same disk of matter around the same star, but they ended up being different planets with different atmospheres and different climates due to their different orbits. So, we would like to understand the fundamental processes of planet formation and evolution using this planetary system.”

Daylan adds that it was a “win-win” to work with Pinglé and Wright on the study.

“As a researcher, I really enjoy interacting with young brains that are open to experimentation and learning and have minimal bias,” he says. “I also think it is very beneficial to high school students, since they get exposure to cutting-edge research and this prepares them quickly for a research career.”

The SRMP was established in 2016 by Or Graur, a former postdoctoral fellow at the Center for Astrophysics | Harvard & Smithsonian. The program accepts about a dozen students per year with priority given to underrepresented minorities.

Thanks to a partnership with the City of Cambridge, the students are paid four hours per week for the research they complete.

“They are salaried scientists,” Sousa-Silva says. “We want to encourage them that pursuing an academic career is enjoyable and rewarding—no matter what they end up pursuing in life.”

Pinglé, a junior in high school, is considering studying applied mathematics or astrophysics after graduation. Wright has just been accepted into a five-year Master of Astrophysics program at the University of Edinburgh in Scotland.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “The Uncertainties in Measuring Cosmic Expansion”

From Harvard-Smithsonian Center for Astrophysics

January 1, 2021

Ninety years after Edwin Hubble discovered the systematic motions of galaxies and George Lemaitre explained them as cosmic expansion from a point using Einstein’s equations of relativity, observational cosmology today is facing a challenge. Values deduced from the two primary methodologies – the properties of galaxies and the cosmic microwave background radiation (CMBR) — disagree with each other at roughly the ten percent level, yet each one is precise at the level of a few percent.

CMB per ESA/Planck

Uncorrected observational errors are possible, but estimates suggest they are too small to account for the differences. As a result, no consistent and precise value of the expansion – Hubble’s constant – has been found. The problem is not so much the value itself – the age of the universe will not change by much either way – rather, it is that something unexplained is clearly going on connected with the fact that the CMBR data arise from a vastly different epoch of cosmic time than do the galaxy data. Perhaps new physics is needed.

An image of distant galaxies as seen by the VIMOS on the ESO Very Large Telescope and WFI on the 2.2 meter MPG/ESO telescope at Cerro La Silla. Two different methods for determining the cosmic rate of expansion of the universe have reached precise but mutually inconsistent results. Astronomers had hoped that a third method that uses gravitational waves would be more accurate, but a new analysis shows that its uncertainties are about as large as in the other methods. Credit: ESO/ Mario Nonino, Piero Rosati and the ESO GOODS Team.

ESO VIMOS on VLT Melipal UT3.

ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
•KUEYEN (UT2; The Moon ),
•MELIPAL (UT3; The Southern Cross ), and
•YEPUN (UT4; Venus – as evening star).
elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo.

Wide Field Imager on the 2.2 meter MPG/ESO telescope at Cerro LaSilla.

MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

An exciting new and independent method of measuring the cosmic expansion parameter uses gravitational waves (GW).

Gravitational waves. Credit: MPI for Gravitational Physics/Werner Benger.

Gravity is talking. Lisa will listen. Dialogos of Eide

ESA/NASA eLISA space based, the future of gravitational wave research.

The observed intensity of the GW provides a measure of the distance since models can infer the intrinsic strength. When the GW results from a binary neutron star merger which has a detected optical counterpart, the host galaxy’s cosmic recession velocity (as measured from its light) provides a calibration for the expansion rate. This new method is called the “standard siren.” If the accuracy of the standard siren method is better than that of the other methods, it would be able to resolve the discrepancy.

CfA astronomer Hsin-Yu Chen has investigated the uncertainties associated with the standard siren method and finds that two issues complicate the standard siren method and pose major challenges to its resolving the tension. Both are related to the emitted light and the viewing angle of the source. The first problem is that the light is not emitted spherically according to computer simulations, and so the intensity we observe depends on our viewing angle; even the color is angle-dependent. The viewing angle must somehow be estimated and included in the calibration, and this carries an uncertainty. The second is that the merger event is also seen from a particular angle that affects the result; even after observing many sources, a statistical analysis of the sample will still have an uncertain bias. Chen concludes that these two systematic effects will introduce a bias in the standard siren value of Hubble’s constant that results in its having an uncertainty that is as about large as the uncertainty in other methods.

Science paper:
Systematic Uncertainty of Standard Sirens from the Viewing Angle of Binary Neutron Star Inspirals
Physical Review Letters

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “A Rosetta Stone for Planet Formation”

From Harvard-Smithsonian Center for Astrophysics

This image shows the disc around the young star AB Aurigae in polarized near-infrared light as seen with the European Very Large Telescope’s SPHERE instrument. Measurements of the molecular components of the disk at millimeter wavelengths reveal several unexpected properties including a warmer temperature, more dust, and a deficiency of sulfur. Credit: ESO/Boccaletti et al.

ESO SPHERE extreme adaptive optics system and coronagraphic facility on the extreme adaptive optics system and coronagraphic facility on the VLT UT3, Cerro Paranal, Chile, with an elevation of 2,635 metres (8,645 ft) above sea level.

ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
•KUEYEN (UT2; The Moon ),
•MELIPAL (UT3; The Southern Cross ), and
•YEPUN (UT4; Venus – as evening star).
elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo.

Planets are formed from the disk of gas and dust around a star, but the mechanisms for doing so are imperfectly understood. Gas is the key driver in the dynamical evolution of planets, for example, because it is the dominant component of the disk (by mass). The timescale over which the gas dissipates sets the timescale for planet formation, yet its distribution in disks is just starting to be carefully measured. Similarly, the chemical composition of the gas determines the composition of the future planets and their atmospheres, but even after decades of studying protoplanetary disks, their chemical compositions are poorly constrained; even the gas-to-dust ratios are largely unknown.

The detailed characterizations of individual sources provide insights into the physical and chemical nature of protoplanetary disks. The star AB Aurigae is a widely studied system hosting a young transitional disk, a disk with gaps suggestive of clearing by newly forming planets. Located 536 light-years (plus-or-minus 1%) from the Sun, it is close enough to be an excellent candidate in which to study the spatial distribution of gas and dust in detail. CfA astronomer Romane Le Gal was a member of a team that used the NOrthern Extended Millimeter Array (NOEMA) to observe the AB Aur gas disk at high spatial resolution in the emission lines of CO, H2CO, HCN, and SO; combined with archival results, their dataset includes a total of seventeen different spectral features.

IRAM NOEMA in the French Alps on the wide and isolated Plateau de Bure at an elevation of 2550 meters, the telescope currently consists of ten antennas, each 15 meters in diameter.interferometer, Located in the French Alpes on the wide and isolated Plateau de Bure at an elevation of 2550 meters.

The scientists, for the first time in a transition disk, mapped the gas density and the gas-to-dust ratio, finding that it was less than expected – half of the interstellar medium value or even in some places as much as four times smaller. Different molecules were seen tracing different regions of the disk, for instance the envelope or the surface. The team measured the average disk temperature to be about 39K, warmer than estimated in other disks. Not least, their chemical analysis determined the relative abundances of the chemicals and found (depending on some assumptions) that sulfur is strongly depleted compared to the solar system value. The new paper’s primary conclusion, that the planet-forming disk around this massive young star is significantly different from expectations, highlights the importance of making such detailed observations of disks around massive stars.

Science paper:
AB Aur, a Rosetta Stone for Studies of Planet Formation I. Chemical study of a planet-forming disk
Astronomy & Astrophysics

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Simulating Meteors with ASMODEUS”

From Harvard-Smithsonian Center for Astrophysics

December 11, 2020

A burst of 1999 Leonid meteors as seen at 38,000 feet from Leonid Multi Instrument Aircraft Campaign. Astronomers have developed a meteor simulation tool to help assess selection biases and evaluate the populations of meteor showers. Credit: NASA/Ames Research Center/ISAS/Shinsuke Abe and Hajime Yano.

A meteor is a rocky or metallic body that enters the Earth’s atmosphere (or the atmosphere of another planet) from space at high speed and burns up; meteors that mostly survive the trip and land on the ground are called meteorites. Meteors have a wide range of sizes and compositions, and meteorites can land pretty much anyplace at any time. Moreover, individual events aren’t repeated. Meteor astronomers must therefore rely on accurate measurements of available observations or statistical processing of large data sets to formulate predictions and theories. The best current models, however, lack firm constraints on key variables like the luminosity of a trail versus the object’s loss of kinetic energy. Performing experiments in meteor science has been considered, but is notoriously difficult. Launching artificial objects, accelerating them to speeds of thousands of miles per hour, recreating the various conditions of meteor entry, and then observing the process of ablation is hard and expensive.

CfA astronomer Peter Veres and his colleagues have developed a cost-effective intermediate solution: a computer simulation that creates virtual meteors based on equations of motion, ablation, and luminosity models whose results can then be examined. The suite of tools the team developed is called ASMODEUS (All-Sky Meteor Optical Detection Efficiency Simulator) and it emphasizes statistical processing of large meteor datasets rather than precision calculations for individual meteors. Several attempts at such simulations had been made before but none included an adequate model of the atmosphere or had the goal of directly comparing the resulting data to observations. The new code includes parameters for the Earth and its atmosphere, meteor material properties, equations for trajectories including gravity and drag and for ablation and luminance; not least, the simulations consider the locations of virtual observers. Of ten thousand simulated meteors, 1354 were “detected.” These included most bright ones, while others (particularly those passing near the horizon) were unlikely to be seen; the distribution of the properties of the simulated meteors was then compared with detection results. The scientists are continuing to improve the code by including more advanced meteoroid dynamics and by addressing the fragmentation of meteors that have fragile compositions. Meanwhile, ASMODEUS can be used to assess selection biases in ground-based observing systems and help evaluate the mass and population character of meteor showers.

Science paper:
“ASMODEUS Meteor Simulation Tool’
Planetary & Space Science

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Artificial Intelligence Classifies Supernova Explosions with Unprecedented Accuracy”

12.17.20

Amy Oliver
Public Affairs
Center for Astrophysics | Harvard & Smithsonian
Fred Lawrence Whipple Observatory
520-879-4406
amy.oliver@cfa.harvard.edu

Cassiopeia A, or Cas A, is a supernova remnant located 10,000 light years away in the constellation Cassiopeia, and is the remnant of a once massive star that died in a violent explosion roughly 340 years ago. This image layers infrared, visible, and X-ray data to reveal filamentary structures of dust and gas. Cas A is amongst the 10-percent of supernovae that scientists are able to study closely. CfA’s new machine learning project will help to classify thousands, and eventually millions, of potentially interesting supernovae that may otherwise never be studied. Credit: NASA/JPL-Caltech/STScI/CXC/SAO.

Artificial intelligence is classifying real supernova explosions without the traditional use of spectra, thanks to a team of astronomers at the Center for Astrophysics | Harvard & Smithsonian. The complete data sets and resulting classifications are publicly available for open use.

By training a machine learning model to categorize supernovae based on their visible characteristics, the astronomers were able to classify real data from the Pan-STARRS1 Medium Deep Survey for 2,315 supernovae with an accuracy rate of 82-percent without the use of spectra.

Pann-STARS 1 Telescope, U Hawaii, situated at Haleakala Observatories on the island of Maui near the summit of Haleakala in Hawaii, USA, altitude 3,052 m (10,013 ft).

The astronomers developed a software program that classifies different types of supernovae based on their light curves, or how their brightness changes over time. “We have approximately 2,500 supernovae with light curves from the Pan-STARRS1 Medium Deep Survey, and of those, 500 supernovae with spectra that can be used for classification,” said Griffin Hosseinzadeh, a postdoctoral researcher at the CfA and lead author on the first of two papers published in The Astrophysical Journal. “We trained the classifier using those 500 supernovae to classify the remaining supernovae where we were not able to observe the spectrum.”

Edo Berger, an astronomer at the CfA explained that by asking the artificial intelligence to answer specific questions, the results become increasingly more accurate. “The machine learning looks for a correlation with the original 500 spectroscopic labels. We ask it to compare the supernovae in different categories: color, rate of evolution, or brightness. By feeding it real existing knowledge, it leads to the highest accuracy, between 80- and 90-percent.”

Although this is not the first machine learning project for supernovae classification, it is the first time that astronomers have had access to a real data set large enough to train an artificial intelligence-based supernovae classifier, making it possible to create machine learning algorithms without the use of simulations.

“If you make a simulated light curve, it means you are making an assumption about what supernovae will look like, and your classifier will then learn those assumptions as well,” said Hosseinzadeh. “Nature will always throw some additional complications in that you did not account for, meaning that your classifier will not do as well on real data as it did on simulated data. Because we used real data to train our classifiers, it means our measured accuracy is probably more representative of how our classifiers will perform on other surveys.” As the classifier categorizes the supernovae, said Berger, “We will be able to study them both in retrospect and in real-time to pick out the most interesting events for detailed follow up. We will use the algorithm to help us pick out the needles and also to look at the haystack.”

The project has implications not only for archival data, but also for data that will be collected by future telescopes. The Vera C. Rubin Observatory is expected to go online in 2023, and will lead to the discovery of millions of new supernovae each year.

NOIRLab Vera C. Rubin Observatory Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,715 m (8,907 ft).

This presents both opportunities and challenges for astrophysicists, where limited telescope time leads to limited spectral classifications.

“When the Rubin Observatory goes online it will increase our discovery rate of supernovae by 100-fold, but our spectroscopic resources will not increase,” said Ashley Villar, a Simons Junior Fellow at Columbia University and lead author on the second of the two papers [The Astrophysical Journal], adding that while roughly 10,000 supernovae are currently discovered each year, scientists only take spectra of about 10-percent of those objects. “If this holds true, it means that only 0.1-percent of supernovae discovered by the Rubin Observatory each year will get a spectroscopic label. The remaining 99.9-percent of data will be unusable without methods like ours.”

Unlike past efforts, where data sets and classifications have been available to only a limited number of astronomers, the data sets from the new machine learning algorithm will be made publicly available. The astronomers have created easy-to-use, accessible software, and also released all of the data from Pan-STARRS1 Medium Deep Survey along with the new classifications for use in other projects. Hosseinzadeh said, “It was really important to us that these projects be useful for the entire supernova community, not just for our group. There are so many projects that can be done with these data that we could never do them all ourselves.” Berger added, “These projects are open data for open science.”

This project was funded in part by a grant from the National Science Foundation (NSF) and the Harvard Data Science Initiative (HDSI).

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Obscured Seyfert Galaxies”

From Harvard-Smithsonian Center for Astrophysics

An optical image of the face-on Seyfet galaxy NGC 3081. The bright nuclei of Seyferts are powered by accretion onto their supermassive balckholes, but circumnuclear dust torii can block our line of sight to optical light. A new study uses hard X-ray emission scattered or reflected from surrounding nuclear structures to analyze the circumnuclear properties of obscured Seyfert nuclei. Credit:NASA/ESA Hubble.

Seyfert galaxies are distinguished by their bright nuclei and radiation from highly ionized atoms. Seyferts look much like quasars, but unlike point-like quasars the Seyfert host galaxies are clearly seen. Astronomers think that the luminous nuclei of Seyferts are powered by accretion of material onto supermassive black holes via a circumnuclear disk, with a dusty torus around them farther away. Different orientations of the disk and obscuring torus to our line of sight are thought to account for the apparent differences seen in Seyfert types, but the morphology and composition of torii are still uncertain and could also play significant roles. For example, some scientists have proposed that the torus is a homogeneous structure, while others argue that it is a clumpy distribution of dense clouds. The accretion of material onto the black hole produces X-ray emission that reflects or scatters off of local structures. This feature can be used to help diagnose the properties of the environment, but much of the X-ray emission, especially at lower energies, is absorbed by obscuring material.

CfA astronomer Laura Brenneman was a member of a team that used the NuSTAR X-ray satellite to study a sample of nineteen optically selected Seyfert galaxies known to have obscuring material along the line of sights to their nuclei.

NASA/DTU/ASI NuSTAR X-ray telescope.

The singular advantage of NuSTAR is its ability to detect high energy X-ray emission that is not blocked. The team additionally used archival observations from several other X-ray missions including Chandra to complete their analysis.

NASA Chandra X-ray Space Telescope

They modeled the optical data with conventional techniques to estimate the black hole masses from the motions of the gas, and used that to model the scattered and reflected X-rays produced by the accretion process to derive the gas densities. They conclude that between 80-90% of the galaxies in their sample have some dense material capable of obscuring the optical light entirely. They also conclude that radiation pressure produced in the accretion processes regulates the distribution of the circumnuclear material, as the less dense material is swept away when accretion rate increases, thereby making the nuclear region less obscured. This new paper represents the first study made of a large controlled sample of Seyferts using hard X-rays to probe the conditions in the heart of Seyfert nuclei.

Science paper:
A Hard Look at Local, Optically Selected, Obscured Seyfert Galaxies
The Astrophysical Journal

See the full article here .

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics via phys.org: “Carbon emission from star-forming clouds”

From Harvard-Smithsonian Center for Astrophysics

via

phys.org

An infrared image taken by the IRAC camera of the young star forming cloud region AGAL313.576+0.324. Regions nominally like this one are known for emitting an infrared line of ionized carbon atom, the result of the ultraviolet light from new stars, however the precise mechanisms are incompletely understood and in extragalactic sources the strength of this line is unpredictable. In a new study of ionized carbon emission in the Milky Way, astronomers found that this particular source stood out for its showing no signs of ionized carbon. Credit: NASA/IRAC.

The carbon atom can be easily ionized, more easily than hydrogen atoms for example. In star forming regions, where massive young stars emit ultraviolet light capable of ionizing atoms, all the neutral carbon nearby becomes ionized. The singly-ionized carbon atom (abbreviated CII) emits a strong line in the far infrared that is both very intense and consequently a reliable proxy for the ultraviolet flux from star formation activity. In some extreme star forming galaxies, the energy in this one infrared CII line alone can be as much as one percent of the entire energy budget of the galaxy. The extreme brightness of the line makes it a very powerful tool for studying cosmically remote galaxies in the early universe because it is one of the easiest lines to detect and its measured wavelength, shifted by expansion of the universe, provides a precise measure of the galaxy’s distance. All this means that astronomers are working towards a more precise understanding of how and where carbon is ionized by young stars. One major outstanding puzzle is that in some bright star-forming galaxies the strength of the CII emission is as much as one hundred or more times weaker than it is in the strongest cases, and the reason is not well understood.

CfA astronomers Howard Smith and Ian Stephens were members of a team that used the SOFIA airborne observatory to study far infrared CII emission in a selection of massive young molecular cloud clumps in our galaxy in the early stages of star formation.

NASA/DLR SOFIA modified Boeing 747 aircraft.

The clumps were selected from previous work of the team that measured and characterized the content and physical properties of over 1200 dark molecular star-forming clumps in the galaxy. In the first SOFIA results, the team measured the CII in four of the clumps. Three of the sources showed bright emission, as expected, and combined with the earlier datasets the spectral information was used to model the properties of the ongoing star formation. But shockingly one of the sources, despite being particularly bright—more than twenty thousand solar-luminosities—had no CII emission at all.

The scientists considered a variety of possible scenarios, from instrumental problems to the presence of abundant foreground cold CII gas that absorbed the emitted light. They even speculate that the clump might be at a much earlier stage of star formation than previously considered. Given only this dataset, however, they were unable to arrive at a definitive conclusion. They have, however, planned a series of follow-up observations to test these and other possibilities. The solution to the puzzle will likely have implications for the extragalactic CII emission strength puzzle.

Science paper:
Characterizing [C ii] Line Emission in Massive Star-forming Clumps
The Astrophysical Journal

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Harvard-Smithsonian Center for Astrophysics: “Feeding a Galaxy’s Nuclear Black Hole”

From Harvard-Smithsonian Center for Astrophysics

A galactic bar is the approximately linear structure of stars and gas that stretches across the inner regions of some galaxies. The bar stretches from one inner spiral arm, across the nuclear region, to an arm on the other side. Found in about half of spiral galaxies, including the Milky Way, bars are thought to funnel large amounts of gas into the nuclear regions, with profound consequences for the region including bursts of star formation and the rapid growth of the supermassive black hole at the center.

Milky Way NASA/JPL-Caltech /ESO R. Hurt. The bar is visible in this image.

Quasars, for example, have been suggested as one result of this kind of activity.

Now iconic image of a quasar.
ESO/M.Kornmesser.

Eventually, however, feedback from such energetic events (supernovae, for example) terminates the inflow and stalls the black hole’s growth. How bars and gas inflows form and evolve are not well understood – galaxy mergers are thought to play a role – nor are the physical properties of galactic nuclei that are still actively accumulating gas. A serious difficulty is that dust in the dense material around the nucleus is opaque to optical radiation and, depending in part on the geometry, can obscure observations. Infrared and submillimeter wavelength measurements that can peer through the dust offer the best way forward.

The luminous, barred galaxy ESO 320-G030 is about one hundred and fifty thousand light-years away and shows no signs of having been in a merger, yet this galaxy has a bar nearly sixty thousand light-years long, as well as a second bar about ten times smaller perpendicular to it. This galaxy shows high star formation activity in the nuclear region, but no clear evidence of an active nucleus, perhaps because of the high extinction. The galaxy is also seen with inflowing gas (and evidence of outflows simultaneously), making it a nearby prototype of isolated, rapidly evolving galaxies driven by their bars.

CfA astronomers Eduardo Gonzalez-Alfonso, Matt Ashby, and Howard Smith led a program of far infrared Herschel spectroscopy of this object coupled with ALMA submillimeter observations of the gas. By carefully modeling the shapes of the infrared absorption lines of water and several of its ionized and isotopic variations, with fifteen other molecular species including ammonia, OH and NH, they conclude that a nuclear starburst of about twenty solar-masses of stars per year is being sustained by gas inflow with short (twenty million year) lifetime. They find evidence for three structural components: an envelope about five hundred light-years across, a dense circumnuclear disk about one hundred twenty light-years in radius, and a compact core or torus forty light-years in size and characterized by its very warm dust. These three components are responsible for about 70% of the galaxy’s luminosity. Although ESO 320-G030 is an exceptional example, being both bright and nearby, the results suggest that similar complex nuclear structures, with inflows and outflows, may be common in luminous galaxies in the more distant universe including those during its most active epoch of star formation.

Science paper:
A Proto-Pseudobulge in ESO 320-G030 Fed by a Massive Molecular Inflow Driven by a Nuclear Bar
Astronomy and Astrophysics

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.