Institute for Gravitation and the Cosmos

2022-08-30

STAR-X, the Survey and Time-domain Astrophysical Research Explorer, a proposed NASA Medium-Class Explorer (MIDEX) mission that includes Penn State astronomer Niel Brandt, has been selected by the NASA Explorers Program for further study. STAR-X is one of two proposed MIDEX missions that will receive $3 million for a nine-month detailed study of mission requirements. At the end of this period, one of the proposed missions will be selected for a target launch date in 2027-2028 and be eligible for up to $300 million in additional funding. Comprised of an X-ray telescope, an ultraviolet (UV) telescope, and a responsive spacecraft, STAR-X is designed to conduct time-domain surveys, which study how astronomical objects change with time, and to respond rapidly to transient cosmic events discovered by other observatories such as LIGO, Rubin LSST, the Roman Space Telescope, and the Square Kilometer Array. The mission is led by Principal Investigator William Zhang at NASA’s Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. Penn State’s Brandt, who is the Verne M. Willaman Professor of Astronomy and Astrophysics and Professor of Physics, is involved in planning the STAR-X cosmic X-ray surveys, active galaxy studies, and fast X-ray transient studies. “I can’t wait to use STAR-X to investigate the first supermassive black holes and understand mysterious, explosive X-ray transient sources,” said Brandt. “STAR-X will also provide the essential X-ray and UV follow-up capabilities for remarkable cosmic objects discovered by the Rubin LSST in optical light.” The STAR-X spacecraft would be able to turn rapidly to point a sensitive wide-field X-ray telescope and a UV telescope at transient cosmic sources, such as supernova explosions and feeding supermassive black holes. Deep X-ray surveys would map black holes and hot gas trapped in distant clusters of galaxies; combined with infrared observations from NASA’s upcoming Roman Space Telescope, these observations would trace how massive clusters of galaxies built up over cosmic history. STAR-X would provide revolutionary capabilities including unprecedented X-ray and UV volumetric survey speed; a unique combination of large field-of-view, large X-ray collecting area, low background, and excellent imaging; increased sensitivity for characterizing diffuse emissions, and increased speed and sensitivity for the discovery of faint X-ray point sources. It fills the gap in X-ray and UV survey coverage, providing simultaneous X-ray and UV observations, which are among the earliest and most uniquely informative astrophysical signals that probe the inner regions around compact objects like black holes and neutron stars, and it complements optical, infrared, and gravitational wave facilities. The mission’s Deputy Principal Investigator, Ann Hornschemeier, who is also Lab Chief for X-ray Astrophysics at GSFC, earned a Ph.D. in Astronomy and Astrophysics at Penn State, mentored by Brandt, in 2002. “Ann is superb - a bundle of energy, and the right person to push STAR-X to succeed,” said Brandt. NASA Explorer missions conduct focused scientific investigations and develop instruments that fill scientific gaps between the agency’s larger space science missions. The proposals were competitively selected based on potential science value and feasibility of development plans. The Explorers Program is the oldest continuous NASA program and is designed to provide frequent, low-cost access to space using principal investigator-led space science investigations relevant to the Science Mission Directorate’s astrophysics and heliophysics programs. “NASA’s Explorers Program has a proud tradition of supporting innovative approaches to exceptional science, and these selections hold that same promise,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at NASA Headquarters in Washington. “From studying the evolution of galaxies to explosive, high-energy events, these proposals are inspiring in their scope and creativity to explore the unknown in our universe.” Since the launch of Explorer 1 in 1958, which discovered the Earth’s radiation belts, the Explorers Program has launched more than 90 missions, including the Uhuru and Cosmic Background Explorer (COBE) missions that led to Nobel prizes for their investigators. The program is managed by NASA Goddard for NASA's Science Mission Directorate in Washington, which conducts a wide variety of research and scientific exploration programs for Earth studies, space weather, the solar system, and the universe. More information can be found at the Explorers Program website (https://explorers.gsfc.nasa.gov/). Further technical details about the observatory are available at (http://star-x.xraydeep.org/observatory/).

2022-07-07

Deep below the Black Hills of South Dakota in the Sanford Underground Research Facility (SURF), an innovative and uniquely sensitive dark matter detector—the LUX-ZEPLIN (LZ) experiment—has passed a check-out phase of startup operations and delivered its first results. The LZ experiment, which is designed to observe the mysterious and as-yet-undetected phenomenon known as dark matter, is led by Lawrence Berkeley National Lab (Berkeley Lab) in conjunction with an international team of 250 scientists and engineers from over 35 institutions including Penn State. “Dark matter is a fundamental part of the universe, but because it does not emit, absorb, or scatter light, it cannot be observed in conventional ways,” said Carmen Carmona-Benitez, assistant professor of physics and the LZ principal investigator at Penn State. “I’m thrilled to see this complex detector ready to address the long-standing mystery of what dark matter is made of. The LZ team now has in hand the most ambitious instrument to do so!” Dark matter’s presence and gravitational pull are fundamental to our understanding of the universe. For example, the presence of dark matter, estimated to be about 85 percent of the total mass of the universe, shapes the form and movement of galaxies, and it is invoked by researchers to explain what is known about the large-scale structure and expansion of the universe. Dark Matter particles have never actually been detected—but perhaps not for much longer. The countdown may have started with results from LZ’s first 60 “live days” of testing. These data were collected over a three-and-a-half-month span of initial operations beginning at the end of December. This was a period long enough to confirm that all aspects of the detector were functioning well. In a paper posted online July 7 on the experiment’s website (https://lz.lbl.gov/) and the online preprint archive arXiv.org, LZ researchers report that with results from the initial run, LZ is the world’s most sensitive dark matter detector. “We plan to collect about 20 times more data in the coming years, so we’re only getting started,” said LZ Spokesperson Hugh Lippincott of the University of California Santa Barbara. “There’s a lot of science to do and it’s very exciting!” A variety of cosmic particles collide with the Earth on a regular basis, and LZ is designed to detect theorized dark matter particles known as weakly interacting massive particles (WIMPs). The experiment is located about a mile underground to protect it from cosmic radiation at the Earth’s surface that could drown out dark matter signals. The heart of the LZ dark matter detector is comprised of two nested titanium tanks filled with ten tons of very pure liquid xenon. When particles collide with xenon atoms, they produce visible scintillation or flashes of light, which are recorded by two arrays of photomultiplier tubes (PMTs), explained Aaron Manalaysay from Berkeley Lab who, as LZ physics coordinator, led the collaboration’s efforts to produce these first physics results, including calibration, understanding of the detector response, and sensitivity. “Considering we just turned it on a few months ago and during COVID restrictions, it is impressive we have such significant results already,” Manalaysay said. The collisions will also knock electrons off xenon atoms, sending them to drift to the top of the chamber under an applied electric field where they produce another flash permitting spatial event reconstruction. “The characteristics of the light signals help determine the types of particles interacting in the xenon, allowing us to separate backgrounds and potential dark matter events,” said Luiz de Viveiros, assistant professor of physics at Penn State, whose team is responsible for modeling and monitoring background signals in the detector. “Lots of subsystems started to come together as we started taking data for detector commissioning, calibrations and science running. Turning on a new experiment is challenging, but we have a great LZ team that worked closely together to get us through the early stages of understanding our detector,” said David Woodward, assistant research professor of physics at Penn State and the experiment run coordinator. The take home message from this successful startup: “We’re ready and everything’s looking good,” said Berkeley Lab Senior Physicist and past LZ Spokesperson Kevin Lesko. “It’s a complex detector with many parts to it and they are all functioning well within expectations,” he said. The design, manufacturing, and installation phases of the LZ detector were led by Berkeley Lab project director Gil Gilchriese. The LZ operations manager, Berkeley Lab’s Simon Fiorucci, said the onsite team deserves special praise at this startup milestone, given that the detector was transported underground late in 2019, just before the onset of the COVID-19 pandemic. He said with travel severely restricted, only a few LZ scientists could make the trip to help on site. The team in South Dakota took excellent care of LZ. "I'd like to second the praise for the team at SURF and would also like to express gratitude to the large number of people who provided remote support throughout the construction, commissioning and operations of LZ, many of whom worked full time from their home institutions making sure the experiment would be a success and continue to do so now,” said Tomasz Biesiadzinski of the SLAC National Accelerator Laboratory and the LZ detector operations manager. “The entire SURF team congratulates the LZ Collaboration in reaching this major milestone," said Mike Headley, executive director of SURF Lab. "The LZ team has been a wonderful partner and we’re proud to host them at SURF.” With confirmation that LZ and its systems are operating successfully, Carmona-Benitez said, it is time for full-scale observations to begin in hopes that a dark matter particle will collide with a xenon atom in the LZ detector soon! LZ is supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics and the National Energy Research Scientific Computing Center, a DOE Office of Science user facility. LZ is also supported by the Science & Technology Facilities Council of the United Kingdom; the Portuguese Foundation for Science and Technology; and the Institute for Basic Science, Korea. Over 35 institutions of higher education and advanced research provided support to LZ. The LZ collaboration acknowledges the assistance of the Sanford Underground Research Facility.

2022-06-21

Though an estimated 100 million black holes are predicted to roam among the stars in our Milky Way galaxy, astronomers have never conclusively identified an isolated black hole – until now. Previously, black holes with the mass of the newly identified one had only been detected in binary systems in which the black hole is gravitationally bound to a normal, visible star. Now, following six years of meticulous observations, NASA’s Hubble Space Telescope has provided, for the first time ever, strong evidence for a lone black hole drifting through interstellar space. A paper describing the discovery, by a team that includes Penn State astronomer Howard Bond, has been accepted for publication in the Astrophysical Journal. “Black holes have been in the news recently as a spectacular image of the black hole at the center of our Milky Way galaxy was released a few weeks ago,” said Bond, professor of practice in astronomy and astrophysics at Penn State. “This black hole has a mass of 4 million times that of our Sun; it's what's called a supermassive black hole. Our object, by contrast, has a mass of only 7.1 times that of the Sun. It's a ‘stellar-mass’ black hole. There are very likely many of these objects in the Milky Way, but they are extremely difficult to detect since they emit no light. Ours is the first one to be identified based on the black hole deflecting the image of a background star that it passed closely in front of.” The black hole that was detected lies about 5,000 light-years away, in the Carina-Sagittarius spiral arm of our galaxy. For context, the nearest star to our solar system, Proxima Centauri, is a little over 4 light-years away. Black holes roaming our galaxy are born from rare, monstrous stars (less than one-thousandth of the galaxy’s stellar population) that are at least 20 times more massive than our Sun. These stars explode as supernovae, and the remnant core is crushed by gravity into a black hole. Because the self-detonation is not perfectly symmetrical, the black hole may get a kick, and go careening through our galaxy like a blasted cannonball. Telescopes can’t photograph a wayward black hole because it doesn’t emit any light. However, a black hole warps space, which then deflects and amplifies starlight from anything that momentarily lines up exactly behind it. Ground-based telescopes, which monitor the brightness of millions of stars in the rich star fields toward the central bulge of our Milky Way, look for such a tell-tale sudden brightening of one of them when a massive object passes between us and the star. Then Hubble follows up on the most interesting such events. Kailash Sahu of the Space Telescope Science Institute in Baltimore, Maryland, along with his team, made the discovery in a survey designed to find just such isolated black holes. The warping of space due to the gravity of a foreground object passing in front of a star located far behind it will briefly bend and amplify the light of the background star as it passes in front of it. The phenomenon, called gravitational microlensing, is used to study stars and exoplanets in the approximately 20,000 events seen so far inside our galaxy. The signature of a foreground black hole stands out as unique among other microlensing events. The very intense gravity of the black hole will stretch out the duration of the lensing event for over 200 days. Next, Hubble was used to measure the amount of deflection of the background star’s image by the black hole. Hubble is capable of the extraordinary precision needed for such measurements. The star’s image was offset from where it normally would be by two milliarcseconds. That’s equivalent to measuring the diameter of a 25-cent coin in Los Angeles as seen from New York City. This astrometric microlensing technique provided information on the mass, distance, and velocity of the black hole. The amount of deflection by the black hole’s intense warping of space allowed the team to estimate it weighs about seven solar masses. The isolated black hole is traveling across the galaxy at 90,000 miles per hour (fast enough to travel from Earth to the moon in less than three hours). That’s faster than most of the other neighboring stars in that region of our galaxy. “Astrometric microlensing is conceptually simple but observationally very tough,” said Sahu. “It is the only technique for identifying isolated black holes.” The existence of stellar-mass black holes has been known since the early 1970's, but all of them--until now--are found in binary star systems. “Detections of isolated black holes will provide new insights into the population of these objects in our Milky Way,” said Sahu. NASA’s upcoming Nancy Grace Roman Space Telescope will discover several thousand microlensing events out of which many are expected to be black holes, and the deflections will be measured with very high accuracy.

2022-03-01

Interested in how scientists collaborate across borders? Or how STEM projects are operated on an international scale? Then check out the upcoming "Crossing Borders to Map Our Universe" seminar this March 21. Anyone can join through Zoom here: https://psu.zoom.us/j/92182953190?pwd=d1Z6QmlReWQ5SUdWanJvWllDbDZ4UT09

Penn State is delighted to serve as a site for the 2023 Conference for Undergraduate Women in Physics.

2022-02-18

Penn State is delighted to serve as a site for the 2023 Conference for Undergraduate Women in Physics. The organizational effort is led by IGC graduate student Unnati Akhouri, together with students Šárka Blahnik and Julian Mintz under the supervision of the local organizing commitee - Prof. Doug Cowen, Prof. Sarah Shandera, Prof. Miguel Mostafá, Prof. Louis Leblond and Prof. Kirstin Purdy-Drew. The effort is backed by the Department of Physics and the Institute for Gravitation and the Cosmos. The committee has also garnered local support from the Eberly College of Science, Department for Astronomy and Astrophysics, MRSEC, Centre for Excellence in Science Education and the student groups Physics and Astronomy for Women+, Society for Physics Students and Towards a More Inclusive Astronomy. The conference will the held January 20-23, 2023 at Penn State. More information about registration and application deadlines will be out soon. We look forward to hosting many accomplished guest speakers and a fantastic cohort of undergraduate physicists!

2022-02-18

The Sloan Foundation has announced that Dr. David Radice, assistant professor of physics and astronomy/astrophysics and member of the IGC, has been selected as a 2022 Sloan Fellow.

2022-02-15

David Radice, assistant professor of physics and of astronomy and astrophysics, has been honored with 2022 Alfred P. Sloan Research Fellowship in recognition of his research accomplishments. Awarded annually since 1955, the fellowship honors extraordinary researchers whose creativity, innovation, and research accomplishments make them stand out as the next generation of scientific leaders. "Today's Sloan Research Fellows represent the scientific leaders of tomorrow," says Adam F. Falk, president of the Alfred P. Sloan Foundation. "As formidable young scholars, they are already shaping the research agenda within their respective fields—and their trailblazing won't end here." Radice is one of 118 outstanding researchers from 51 institutions across the U.S. and Canada to make up this year’s cohort. The fellowships are awarded in close coordination with the scientific community. Candidates must be nominated by their fellow scientists and winners are selected by independent panels of senior scholars on the basis of a candidate’s research accomplishments, creativity, and potential. A Sloan Research Fellowship is one of the most prestigious awards available to young researchers. Radice focuses his research on the study of explosive astrophysical events that produce gravitational waves and light, such as neutron-star mergers and core-collapse supernovae. His research makes use of large-scale supercomputing simulations. He is also interested in the development of new computational techniques and in the understanding of fundamental physics questions such as the nature of turbulence. Radice’s honors and awards include an Early Career Research Program Award from the Department of Energy in 2020, a Giulio Rampa Thesis Prize from the University of Pavia in 2014, and a Prize Postdoctoral Fellowship from the California Institute of Technology in 2013. Prior to joining the faculty at Penn State, Radice was an associate research scholar at Princeton University and at the Institute for Advanced Study from 2016 to 2019 and a Walter Burke Fellow in Theoretical Astrophysics and Relativity at the California Institute of Technology from 2013 to 2016. He earned a doctoral degree in gravitational wave astronomy at the Max Planck Institute for Gravitational Physics, Germany, in 2013 and master’s and bachelor’s degrees in mathematical engineering at Politecnico di Milanoin Italy in 2009 and 2006, respectively.

2022-02-04

IGC member B.S. Sathyaprakash was a co-chair of the Science Team of the Gravitational Wave International Committee, charged to develop a vision for the next generation of ground-based gravitational wave detectors.

2022-01-18

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.

Stephanie Wissel has been selected for the Downsbrough Early Career Professor in Physics!

2022-01-18

We are delighted to announce that Dr. Stephanie Wissel, assistant professor of physics and astronomy/astrophysics, has been selected for the Downsbrough Early Career Professor in Physics! Stephanie works in experimental astro-particle physics with expertise in the detection and study of cosmic neutrinos. She’s pursuing the discovery of cosmogenic and astrophysical neutrinos at ultra-high energies (greater than 100 PeV) using radio detection techniques. These experiments will provide unprecedented insight into Nature’s highest energy accelerators and into the physics of extreme environments such as pulsars, gamma-ray bursts, and active galactic nuclei. Stephanie also plays a key role in our department’s educational, service, and outreach missions, including taking leadership in our efforts to build an inclusive, diverse community of graduate students and postdocs. Please join us in congratulating Stephanie on this well-deserved honor!

2022-01-15

The series will consist of 6 public lectures, held on consecutive Saturdays via Zoom.