From The University of California-Riverside
12.6.23
Iqbal I Pittalwala
Senior Public Information Officer
iqbal.pittalwala@ucr.edu
(951) 827-6050
UC Riverside study reports dark matter may be more vibrant than previously thought.
Thought to make up 85% of matter in the universe, dark matter is nonluminous and its nature is not well understood. While normal matter absorbs, reflects, and emits light, dark matter cannot be seen directly, making it harder to detect. A theory called “self-interacting dark matter,” or SIDM, proposes that dark matter particles self-interact through a dark force, strongly colliding with one another close to the center of a galaxy.
In work published in The Astrophysical Journal Letters [below], a research team led by Hai-Bo Yu, a professor of physics and astronomy at the University of California, Riverside, reports that “SIDM” simultaneously can explain two astrophysics puzzles in opposite extremes.
“The first is a high-density dark matter halo in a massive elliptical galaxy,” Yu said. “The halo was detected through observations of strong gravitational lensing, and its density is so high that it is extremely unlikely in the prevailing cold dark matter theory.
The second is that dark matter halos of ultra-diffuse galaxies have extremely low densities and they are difficult to explain by the cold dark matter theory.”
A dark matter halo is the halo of invisible matter that permeates and surrounds a galaxy or a cluster of galaxies.
Gravitational lensing takes place when light traveling across the universe from distant galaxies gets bent around massive objects. The cold dark matter, or CDM, paradigm/theory assumes dark matter particles are collisionless. As their name suggests, ultra-diffuse galaxies have extremely low luminosity and the distribution of their stars and gas is spread out.
Yu was joined in the study by Ethan Nadler, a joint postdoctoral fellow at the Carnegie Observatories and University of Southern California, and Daneng Yang, a postdoctoral scholar at UCR.
To show “SIDM” can explain the two astrophysics puzzles, the team conducted the first high-resolution simulations of cosmic structure formation with strong dark matter self-interactions on relevant mass scales for the strong lensing halo and ultra-diffuse galaxies.
“These self-interactions lead to heat transfer in the halo, which diversifies the halo density in the central regions of galaxies,” Nadler said. “In other words, some halos have higher central densities, and others have lower central densities, compared to their CDM counterparts, with details depending on the cosmic evolution history and environment of individual halos.”
According to the team, the two puzzles pose a formidable challenge to the standard CDM paradigm.
“CDM is challenged to explain these puzzles,” Yang said. “’SIDM’ is arguably the compelling candidate to reconcile the two opposite extremes. No other explanations are available in the literature. Now there is an intriguing possibility that dark matter may be more complex and vibrant than we expected.”
The research also demonstrates the power of probing dark matter through astrophysical observations, with the tool of computer simulations of cosmic structure formation.
“We hope our work encourages more studies in this promising research area,” Yu said. “It will be a particularly timely development given the expected influx of data in the near future from astronomical observatories, including the James Webb Space Telescope and upcoming Rubin Observatory.”
Since around 2009, work by Yu and collaborators has helped popularize “SIDM” in the particle physics and astrophysics communities.
The research was supported by the John Templeton Foundation and the U.S. Department of Energy.
The Astrophysical Journal Letters
See the science paper for instructive material with images. APJL has made images in this paper proprietary and not reproducible.
See the full article here .
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The University of California-Riverside is a public land-grant research university in Riverside, California. It is one of the 10 campuses of The University of California system. The main campus sits on 1,900 acres (769 ha) in a suburban district of Riverside with a branch campus of 20 acres (8 ha) in Palm Desert. In 1907, the predecessor to The University of California-Riverside was founded as the UC Citrus Experiment Station, Riverside which pioneered research in biological pest control and the use of growth regulators responsible for extending the citrus growing season in California from four to nine months. Some of the world’s most important research collections on citrus diversity and entomology, as well as science fiction and photography, are located at Riverside.
The University of California-Riverside is now a member of the Association of American Universities.
The University of California-Riverside ‘s undergraduate College of Letters and Science opened in 1954. The Regents of the University of California declared The University of California-Riverside a general campus of the system in 1959, and graduate students were admitted in 1961. To accommodate an enrollment of 21,000 students by 2015, more than $730 million has been invested in new construction projects since 1999. Preliminary accreditation of the The University of California-Riverside School of Medicine was granted in October 2012 and the first class of 50 students was enrolled in August 2013. It is the first new research-based public medical school in 40 years.
The University of California-Riverside is classified among “R1: Doctoral Universities – Very high research activity.” The U.S. News & World Report Best Colleges rankings places UC-Riverside highly among top public universities and among all universities nationwide. The University of California-Riverside ‘s academic programs, including the Graduate School of Education and the Bourns College of Engineering, are highly ranked nationally based on peer assessment, student selectivity, financial resources, and other factors. Washington Monthly ranked The University of California-Riverside very high in the United States in terms of social mobility, research and community service, while U.S. News ranks The University of California-Riverside as highly ethnically diverse and, by the number of undergraduates receiving Pell Grants, among the most economically diverse student bodies in the nation. Over 70% of all The University of California-Riverside students graduate within six years without regard to economic disparity. The University of California-Riverside ‘s extensive outreach and retention programs have contributed to its reputation as a “university of choice” for minority students. In 2005, The University of California-Riverside became the first public university campus in the nation to offer a gender-neutral housing option. The University of California-Riverside’s sports teams are known as the Highlanders and play in the Big West Conference of the National Collegiate Athletic Association (NCAA) Division I. Their nickname was inspired by the high altitude of the campus, which lies on the foothills of Box Springs Mountain. The University of California-Riverside women’s basketball team won back-to-back Big West championships in 2006 and 2007. In 2007, the men’s baseball team won its first conference championship and advanced to the regionals for the second time since the university moved to Division I in 2001.
History
At the turn of the 20th century, Southern California was a major producer of citrus, the region’s primary agricultural export. The industry developed from the country’s first navel orange trees, planted in Riverside in 1873. Lobbied by the citrus industry, the University of California Regents established the UC Citrus Experiment Station (CES) on February 14, 1907, on 23 acres (9 ha) of land on the east slope of Mount Rubidoux in Riverside. The station conducted experiments in fertilization, irrigation and crop improvement. In 1917, the station was moved to a larger site, 475 acres (192 ha) near Box Springs Mountain.
The 1944 passage of the GI Bill during World War II set in motion a rise in college enrollments that necessitated an expansion of the state university system in California. A local group of citrus growers and civic leaders, including many University of California-Berkeley alumni, lobbied aggressively for a University of California -administered liberal arts college next to the Citrus Experiment Station. State Senator Nelson S. Dilworth authored Senate Bill 512 (1949) which former Assemblyman Philip L. Boyd and Assemblyman John Babbage (both of Riverside) were instrumental in shepherding through the State Legislature. Governor Earl Warren signed the bill in 1949, allocating $2 million for initial campus construction.
Gordon S. Watkins, dean of the College of Letters and Science at The University of California-Los Angeles, became the first provost of the new college at Riverside. Initially conceived of as a small college devoted to the liberal arts, he ordered the campus built for a maximum of 1,500 students and recruited many young junior faculty to fill teaching positions. He presided at its opening with 65 faculty and 127 students on February 14, 1954, remarking, “Never have so few been taught by so many.”
The University of California-Riverside’s enrollment exceeded 1,000 students by the time Clark Kerr became president of the University of California system in 1958. Anticipating a “tidal wave” in enrollment growth required by the baby boom generation, Kerr developed the California Master Plan for Higher Education and the Regents designated Riverside a general university campus in 1959. The University of California-Riverside’s first chancellor, Herman Theodore Spieth, oversaw the beginnings of the school’s transition to a full university and its expansion to a capacity of 5,000 students. The University of California-Riverside’s second chancellor, Ivan Hinderaker led the campus through the era of the free speech movement and kept student protests peaceful in Riverside. According to a 1998 interview with Hinderaker, the city of Riverside received negative press coverage for smog after the mayor asked Governor Ronald Reagan to declare the South Coast Air Basin a disaster area in 1971; subsequent student enrollment declined by up to 25% through 1979. Hinderaker’s development of innovative programs in business administration and biomedical sciences created incentive for enough students to enroll at University of California-Riverside to keep the campus open.
In the 1990s, The University of California-Riverside experienced a new surge of enrollment applications, now known as “Tidal Wave II”. The Regents targeted The University of California-Riverside for an annual growth rate of 6.3%, the fastest in The University of California system, and anticipated 19,900 students at The University of California-Riverside by 2010. By 1995, African American, American Indian, and Latino student enrollments accounted for 30% of The University of California-Riverside student body, the highest proportion of any University of California campus at the time. The 1997 implementation of Proposition 209—which banned the use of affirmative action by state agencies—reduced the ethnic diversity at the more selective UC campuses but further increased it at The University of California-Riverside.
With The University of California-Riverside scheduled for dramatic population growth, efforts have been made to increase its popular and academic recognition. The students voted for a fee increase to move The University of California-Riverside athletics into NCAA Division I standing in 1998. In the 1990s, proposals were made to establish a law school, a medical school, and a school of public policy at The University of California-Riverside, with The University of California-Riverside School of Medicine and the School of Public Policy becoming reality in 2012. In June 2006, The University of California-Riverside received its largest gift, $15.5 million from two local couples, in trust towards building its medical school. The Regents formally approved The University of California-Riverside’s medical school proposal in 2006. Upon its completion in 2013, it was the first new medical school built in California in 40 years.
Academics
As a campus of The University of California system, The University of California-Riverside is governed by a Board of Regents and administered by a president. The University of California-Riverside ‘s academic policies are set by its Academic Senate, a legislative body composed of all UC-Riverside faculty members.
The University of California-Riverside is organized into three academic colleges, two professional schools, and two graduate schools. The University of California-Riverside’s liberal arts college, the College of Humanities, Arts and Social Sciences, was founded in 1954, and began accepting graduate students in 1960. The College of Natural and Agricultural Sciences, founded in 1960, incorporated the Citrus Experiment Station as part of the first research-oriented institution at The University of California-Riverside; it eventually also incorporated the natural science departments formerly associated with the liberal arts college to form its present structure in 1974. The University of California-Riverside ‘s newest academic unit, the Bourns College of Engineering, was founded in 1989. Comprising the professional schools are the Graduate School of Education, founded in 1968, and The University of California-Riverside School of Business, founded in 1970. These units collectively provide 81 majors and 52 minors, 48 master’s degree programs, and 42 Doctor of Philosophy (PhD) programs. The University of California-Riverside is the only UC campus to offer undergraduate degrees in creative writing and public policy and one of three UCs (along with The University of California-Berkeley and The University of California-Irvine) to offer an undergraduate degree in business administration. Through its Division of Biomedical Sciences, founded in 1974, The University of California-Riverside offers the Thomas Haider medical degree program in collaboration with The University of California-Los Angeles. The University of California-Riverside ‘s doctoral program in the emerging field of dance theory, founded in 1992, was the first program of its kind in the United States, and The University of California-Riverside ‘s minor in lesbian, gay and bisexual studies, established in 1996, was the first undergraduate program of its kind in the University of California system. A new BA program in bagpipes was inaugurated in 2007.
Research and economic impact
Overall, monies spent at The University of California-Riverside have an economic impact of nearly $1 billion in California. Total research expenditures at The University of California-Riverside are significantly concentrated in agricultural science. Top research centers by expenditure include the Agricultural Experiment Station; the Center for Environmental Research and Technology; the Center for Bibliographical Studies; the Air Pollution Research Center; and the Institute of Geophysics and Planetary Physics.
Throughout The University of California-Riverside ‘s history, researchers have developed more than 40 new citrus varieties and invented new techniques to help the $960 million-a-year California citrus industry fight pests and diseases. In 1927, entomologists at the CES introduced two wasps from Australia as natural enemies of a major citrus pest, the citrophilus mealybug, saving growers in Orange County $1 million in annual losses. This event was pivotal in establishing biological control as a practical means of reducing pest populations. In 1963, plant physiologist Charles Coggins proved that application of gibberellic acid allows fruit to remain on citrus trees for extended periods. The ultimate result of his work, which continued through the 1980s, was the extension of the citrus-growing season in California from four to nine months. In 1980, The University of California-Riverside released the Oroblanco grapefruit, its first patented citrus variety. Since then, the citrus breeding program has released other varieties such as the Melogold grapefruit, the Gold Nugget mandarin (or tangerine), and others that have yet to be given trademark names.
To assist entrepreneurs in developing new products, The University of California-Riverside is a primary partner in the Riverside Regional Technology Park, which includes the City of Riverside and the County of Riverside. It also administers six reserves of the University of California Natural Reserve System. UC-Riverside recently announced a partnership with China Agricultural University[中国农业大学](CN) to launch a new center in Beijing, which will study ways to respond to the country’s growing environmental issues. University of California-Riverside can also boast the birthplace of two-name reactions in organic chemistry, the Castro-Stephens coupling and the Midland Alpine Borane Reduction.
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