The astrophysics community recently celebrated the first direct image of a supermassive black hole by the Event Horizon Telescope. We know that the black hole they studied, the one at the center of the galaxy Messier 87 (or M87) in the Virgo Galaxy Cluster, is around six billion times as massive as our own sun, but how did it accumulate so much mass and, more generally, how and when did these massive black holes form?
Jan 30, 2020 | Taking on the blending challenge
One of the biggest challenges facing researchers who will use data from the Legacy Survey of Space and Time (LSST) provided by the Vera C. Rubin Observatory (VRO—formerly the Large Synoptic Survey Telescope) is that, as it scans the sky from its perch on a mountain top in the Chilean Andes, it will see a crowded Universe. A significant number of objects in LSST images will appear to overlap to some extent—galaxies with galaxies, stars with stars, galaxies with stars—creating uncertainties in shapes and redshifts.
Dec 6, 2019 | ICYMI: A day in the life of a cosmic-ray 'bookkeeper'
Early-career physicist Jonathan LeyVa helps build one of the world’s most sensitive dark matter detectors. LeyVa works in a clean room at the Department of Energy's SLAC National Accelerator Laboratory, where crews are building detectors for the latest in a series of Super Cryogenic Dark Matter Search (SuperCDMS) experiments. As an early-career physicist, part of his job is keeping track of how much exposure to cosmic rays—high-energy particles falling in from space—the detector components are getting. Researchers want to keep that exposure to a minimum because it could harm their ability to detect dark matter later on.
The Dark Energy Spectroscopic Instrument (DESI) is a new instrument mounted on a telescope in Arizona. On Oct. 22, it aimed its robotic array of 5,000 fiber-optic “eyes” at the night sky to capture the first images showing its unique view of galaxy light. It was the first test of a long-awaited instrument designed to explore the mystery of dark energy, which makes up about 68 percent of the universe and is speeding up its expansion.
A team of Stanford University researchers are on a mission to identify dark matter once and for all. But first, they’ll need to build the world’s most sensitive radio.
May 30, 2019 | Where are they now? Kate Follette
In the occasional series, "Where are they now?" we check in with KIPAC alumni: where they are now, how they've fared since their days exploring particle astrophysics and cosmology at the Institute, and how their KIPAC experiences have shaped their journeys. Next up is Kate Follette, an alum of Professor Bruce Macintosh's exoplanet group, where she searched for young exoplanets and protoplanetary disks (aka planet nurseries), in large part using data from the Gemini Planetary Imager (GPI). She's now an assistant professor of astronomy at Amherst College in Amherst, Massachusetts, where she teaches astronomy. She also teaches about those exoplanets she's still searching for.
Apr 14, 2019 | Extreme energy bullets from mini-black hole jets
A microquasar is an active collapsed star, such as a small black hole or a neutron star, which is accreting the material of a more normal companion star. It has jets or particles that shoot out along its poles and an accretion disk of hot material circling it, and is essentially a smaller cousin of Nature’s most violent objects, active galactic nuclei (AGN).
The model that currently best describes evolution and structure of the Universe (referred to as Lambda-CDM or LCDM) is consistently in agreement qualitatively and quantitatively with virtually all observations we make. And with the enormous increase in the amount of data coming from different cosmic probes (for example, Type Ia supernovae, galaxy surveys, gravitational lensing, the cosmic microwave background [CMB], etc.), our ability to extensively cross-check results and improve our theoretical understanding is only growing. But LCDM isn’t perfect, and when multiple independent measurements of the same parameter are involved, there arises the distinct possibility of finding results that are in tension with each other—the measurements don’t match up, even when error bars are taken into account.
Since 1998, analyses of supernovae data have shown that our Universe has been undergoing accelerated expansion in the latter part of its life. Because ordinary matter can only provide an attractive force, there must be something else providing the repulsive force to accelerate the Universe's expansion. We call the unknown driver of this expansion dark energy—and the question of its origin is a core issue in cosmology and fundamental physics today.
Jan 30, 2019 | Where do the highest-energy cosmic rays come from?
A century after the discovery of cosmic rays, delving into their mysteries remains a primary focus of high-energy astrophysics. Cosmic rays consist of energetic particles propagating through interstellar and even intergalactic space, and are characterized by an energy spectrum extending over at least eleven orders of magnitude, from ~1 GeV (giga-electronvolt, a commonly used unit of energy in astrophysics) to extreme energies of about 1011 GeV (for comparison, the mass of a proton when converted to an equivalent energy via E=mc2 is just under 1 GeV—so those highest-energy cosmic rays have about the energy of a fastball packed sometimes into one elementary particle!).
Halos are the result of a long sequence of cosmic structure formation. We think it happened like this: The early Universe, after a very short period of rapid expansion called inflation, settled into its current phase of more leisurely general cosmic expansion (or “Hubble flow,” as cosmologists often call it). At the end of inflation, while the density of dark matter—on average—had been smoothed out to become very homogenous on large scales, small quantum perturbations were amplified to more significant density fluctuations—places where there was a tiny bit more, or less, matter. The knots of slightly higher density served as wells of gravitational potential and began to grow further with time by attracting ever more matter through gravity.
In the centers of most galaxies lurk gigantic black holes, millions to billions of times the mass of the sun. Most of them are just minding their own business, but in about 10% of cases they are actively consuming matter and transforming much of it into vast amounts of energy. We call these gluttons “quasars”—supermassive black holes surrounded by bright, hot disks of gas called accretion disks. Although quasars are among the most luminous objects in the Universe, we still do not understand the detailed physics of how this matter behaves. This is now changing thanks to new insights and advances from an unexpected source: the highly sensitive timing satellites used to search for planets around other stars by continuously monitoring their brightness over time, to search for periodic dips caused by transiting planets.