JILA Sites: JILA Physics Frontier Center JILA Members
Jupiter is large enough to fit 1,300 Earths inside, and still have room. But like all planets, Jupiter was once nothing more than a cosmic dust bunny.
A team of physicists at JILA and the University of Arizona, led by JILA Senior Research Associate Jake Simon, are studying how cosmic pebbles—starting only a millimeter in size—can lead to the formation of planetesimals, the football-...
The Sun isn’t working the way we thought it did. Many astrophysicists haven't actually understood one aspect of how the Sun worked––until former senior research associate Nick Featherstone and senior research associate Brad Hindman set the record straight.
Stars like the Sun have to get rid of the heat generated by thermonuclear reactions in their centers. The Sun’s secret is vigorous...
Eric Coughln has been named winner of the 2016 Ph.D. Thesis Prize from the High Energy Phenomena and Fundamental Physics Division of the International Astronomical Union. He will receive the prize at the next IAU General Assemply, which will be held in Vienna in August 2018. Coughlin is also winner of the 2017 Dissertation Prize from the High Energy Astrophysics Division of the American...
The lovely Crab Nebula was created by a supernova and its spinning-neutron-star remnant known as a pulsar. Pulsar wind nebulae, such as the Crab, shine because they contain plasmas of charged particles, such as electrons and positrons, traveling at near the speed of light. A key question in astrophysics has long been: What process accelerates some of the charged particles in plasmas to...
Deborah Jin and Katharine Gebbie are two of 10 prominent scientists featured in "Gone in 2016: Notable Women in Science and Technology" written by Maia Weinstock. The article appeared online in Scientific American blogs on December 28, 2016. Jin, who died on September 15, 2016 at age 47, was a visionary researcher in ultracold atomic physics. Gebbie, who died on August 17 at age 84,...
Astrophysicist Jeff Linsky and his colleagues recently created a sophisticated mathematical model of the outer atmosphere of the small M-dwarf star called GJ832. The new model fits well with spectral observations of the star made with the Hubble Space Telescope (HST). This accomplishment bodes well for two reasons: First, it provides a tool for better understanding M-dwarf stars––the most...
Galaxy mergers routinely occur in our Universe. And, when they take place, it takes years for the supermassive black holes at their centers to merge into a new, bigger supermassive black hole. However, a very interesting thing can happen when two black holes get close enough to orbit each other every 3–4 months, something that happens just before the two black holes begin their final desperate...
Fellow Mitch Begelman’s new theory says it’s possible to form stars while a supermassive black hole consumes massive amounts of stellar debris and other interstellar matter. What’s more, there’s evidence that this is exactly what happened around the black hole at the center of the Milky Way some 4–6 million years ago, according to Associate Fellow Ann-Marie Madigan.
Relatively recently...
Graduate student Greg Salvesen, JILA Collaborator Jake Simon (Southwest Research Institute), and Fellows Phil Armitage and Mitch Begelman decided they wanted to figure out why swirling disks of gas (accretion disks) around black holes often appear strongly magnetized. They also wanted to figure out the mechanism that allowed this magnetization to persist over time. In the process, they hoped...
Fellow Phil Armitage and group collaborator Jacob Simon of the Southwest Research Institute are leading work to answer a central question about planet formation: How do pea- and pebble-sized objects orbiting within a protoplanetary disk evolve into asteroid-sized objects tens to hundreds of kilometers in size? This is an important question to answer because the eventual formation of planets...
In 2008, Fellow Jeff Linsky and his colleague Seth Redfield of Wesleyan University used spectral information gathered by the Hubble Space Telescope to figure out that the solar system is surrounded by 15 nearby clouds of warm gas, all within 50 light years of the Sun. In 2014, Cécile Gry of Aix-Marseille Université (France) and Edward Jenkins of Princeton University Observatory analyzed the...
Fellow Phil Armitage and his collaborator Jake Simon of the Southwest Research Institute recently conducted a theoretical study of turbulence in the outer reaches of an accretion disk around HD 163296, a nearby young star. Meanwhile, the Atacama large Millimeter/submillimeter Array (ALMA) in northern Chile observed the same accretion disk. There were intriguing and unexpected differences...
Ever wondered how magnetic pressure alone might be able to maintain the structure of an accretion disk around a black hole in an x-ray binary system? Fellow Mitch Begelman recently gave the idea a lot of thought. And, in the process of working on the idea with Fellow Phil Armitage and Chris Reynolds of the University of Maryland, Begelman came up with a new model for accretion disks around...
When an ordinary star like our Sun wanders very close to a supermassive black hole, it’s very bad news for the star. The immense gravitational pull of the black hole (i.e., tidal forces) overcomes the forces of gravity holding the star together and literally pulls the star apart. Over time, the black hole swallows half of the star stuff, while the other half escapes into the interstellar...
Graduate student Benjamin Greer has won the 2015 R. N. Thomas Award. The $500 award comes from a fund established by Nora Thomas, the widow of JILA co-founder Dick Thomas. Greer also received a book about Thomas’ storied career in astrophysics.
Greer is a fifth-year graduate student in Astrophysical and Planetary Sciences who plans to graduate in December. He works under Fellow Juri...
For astrophysicists like Fellow Jeff Linsky, the Lyman-α spectral line of atomic hydrogen is a powerful tool for investigating the stellar winds emitted by stars, the deuterium/hydrogen (D/H) ratio in the Galaxy, the excited states of hydrogen molecules and carbon monoxide in the environments around young stars, and photochemical processes that create oxygen in the atmospheres of planets...
Supermassive black holes at the center of active galaxies are known as blazars when they are extremely bright and produce powerful jets of matter and radiation visible along the line of sight to the Earth. Blazars can appear up to a thousand times more luminous than ordinary galaxies, and their associated jets are so powerful they can travel millions of light years across the Universe. Blazar...
A Be star is a luminous, blue B-type star with distinctive spectral lines that can provide two types of feasts (tasty snacks or full-scale banquets) for a former companion star in a binary system. The feasting begins when the companion star goes supernova and becomes a neutron star or, more rarely, a black hole. Typically, the companion blows up with enough force to kick itself into an...
Fellows Mitch Begelman and Phil Armitage have just solved the 40-year old mystery of what causes the gas of stellar debris surrounding black holes in binaries to flip back and forth cyclically between a spherical cloud and a luminous disk.
When stellar-sized black holes orbit around another star, the black holes feed themselves by pulling material off their companion stars, funneling it...
Black holes have a new item on their dinner menu: a three-dimensional glowing sphere of stellar debris that looks like a star. The sphere provides a sumptuous main course for a supermassive black hole, while emitting excess energy via jets erupting from its polar regions. The idea for this new type of gourmet feast for black holes comes compliments of graduate student Eric Coughlin and Fellow...
What sets the stage for planet formation?
To search for answers to this question, research associate Jake Simon and his colleagues are performing a series of high-level computer simulations of the outer disks around young stars such as TW Hydrae, shown here. Simon’s daunting task is being facilitated with new information that has just started to come in from the Atacama Large Millimeter...
Susanna Kohler has won this year's Richard N. Thomas award, given in honor of the late Dick Thomas, co-founder of JILA. The award honors an outstanding JILA graduate student in astrophysical and planetary sciences. It was presented to Kohler on May 17, 2013, by Nora Thomas, widow of Dick Thomas. Congratulations, Susanna!
Astrophysicist Fellow Jeff Linsky and his colleagues from CU’s Center for Astrophysics and Space Astronomy have come up with a neat strategy for helping to determine whether an exoplanet’s atmosphere contains evidence of Earth-like life. The first step is to see whether an exoplanet’s atmosphere contains oxygen (O2), ozone (O3), or other molecules that could have been...
Fellow Mitch Begelman and colleague Marek Sikora of the Polish Academy of Sciences have proposed a solution for the long-standing puzzle of what causes black holes to launch powerful jets. Jets are extremely energetic material (plasma) traveling at very close to the speed of light and spanning distances of thousands to hundreds of thousands of light years. The dominant factor in the creation...
Research associate Bruno Giacomazzo recently studied the effects of magnetic fields and matter on the likelihood that the merger of two black holes will produce jets of light of different frequencies ranging from radio waves to X-rays. If such signals are generated, it may be possible to detect them with ground- or space-based observatories. Their detection would help astronomers identify...
Many neutron stars are surrounded by accretion disks. The disks are often made up of matter pulled in by the neutron star’s gravity from a companion star in a binary system. Over time, the neutron stars can swallow so much additional material that they collapse into black holes.
Recently, research associate Bruno Giacomazzo and Fellow Rosalba Perna studied this collapse process in...
Fellow Mitch Begelman and his colleagues came up with the idea of quasistars to explain the origin of the supermassive black holes found at the center of most galaxies. According to Begelman, quasistars formed when massive amounts of gas were funneled into the center of protogalaxies. This prodigious amount of gas collapsed directly into black holes without forming stars. The resulting black...
Giant planets form inside a disk of gas and dust orbiting a new star. At first, gravitational interactions between the disk and the planets will keep planetary orbits circular, according to Fellow Phil Armitage. But, once the disk begins to disperse, things get very interesting.
Over millions of years, X-rays emitted by the central star evaporate the protoplanetary disk until it...
On Earth, people use enormous linear accelerators and synchrotrons for such purposes as high-energy physics experiments, chemical composition analysis, and drug research. Linear accelerators ramp up the speeds of electrons and other charged subatomic particles close to the speed of light. Synchrotrons also accelerate charged particles (in a circular track) that, when deflected through...
Some stars die dramatically – the light from the supernova explosion of a distant massive star can outshine an entire galaxy. But this event isn’t the endgame for the star — the dense remnants of some of these explosions (called neutron stars) can spit out light rays over thousands of years.
Astronomers have noticed that some of these neutron stars emit bursts of high-energy light...
The Solar System has a remarkable number of planets. It includes four rocky planets (Mercury, Venus, Earth, and Mars), four giant gaseous planets, and countless smaller worlds. Early on, there may even have been a fifth rocky planet that collided with the Earth, forming the Moon. We owe the survival of so many terrestrial planets (and our own evolution as a species) to the...
Long, long ago galaxies now far away formed around ravenous black holes scattered throughout the Universe. Some 12.5 billion years later, JILA scientist Gayler Harford and Fellow Andrew Hamilton have identified the superhighways that funneled gas into some of the nascent galaxies. These thruways not only routed gas to feed the monster black holes, but also supplied raw materials for the...
Supernova 1987A is illuminating its own past. The brightest supernova to light up Earth’s night skies since the Renaissance, it appeared in the southern sky on February 23, 1987 when a blue supergiant star exploded in the Large Magellanic Cloud, a galaxy located 160,000 light years from Earth. For nearly 25 years, Fellow Dick McCray and his colleagues have studied the unfolding story...
The Cosmic Origins Spectrograph, or COS, is a powerful new instrument scanning the Universe. COS was installed on the Hubble Space Telescope in 2009. Since then, it has been searching for clues about the composition of the Universe, including how galaxies like our own Milky Way formed and evolved over time. It is seeing beautiful things never before detected in the Universe because it is the...
Hot Jupiters — giant gas planets orbiting close to their parent stars — aren’t just scorched (at temperatures of >1000 K). They are also swollen up larger than can be explained by the intense heat from their host stars. Recently Fellow Rosalba Perna and her colleagues from Columbia University and the Kavli Institute for Theoretical Physics suggested a reason...
There are two competing ideas about the origin of the monster black holes at the center of galaxies. Both include exceptional stars that have never actually been observed: (1) massive population III (Pop III) stars (as big as a thousand Suns) made of pure hydrogen and helium that would have formed less than 100 million years after the Big Bang, and (2) gigantic quasistars whose shining...
Senior research associate Brad Hindman of the Toomre group uses helioseismology to understand what’s happening under the surface of the Sun. Helioseismology is a lot like the ultrasound tests used to evaluate medical conditions. However, there’s a big difference: physicians already have a good idea of the basic structures they are probing with sound waves. Helioseismologists don...
A faint star that can easily be seen from Earth with binoculars has a Jupiter-like gas planet orbiting it once in just three days. That means the planet is close enough to its Sun-like star to get scorching hot, which affects both the planet and its atmosphere. The star is called HD209458, and its planet’s moniker is HD209458b.
Recently Fellow Jeff Linsky, research...
Fellow Phil Armitage and colleagues from the Université de Bordeaux and Google, Inc. are key players in the quest to understand the secrets of planet formation. Current theory posits that there are three zones of planet formation around a star (as shown in the figure). In Zone One, the hot innermost zone, small rocky planets form over a period of hundreds of millions of years. The...
Fellow Phil Armitage studies the migration of gas giant planets through evolving protoplanetary disks. He and former JILA postdoc Richard Alexander (Universiteit Leiden) have designed relatively simple models that reproduce the observed frequency and distribution of extra-solar giant planets, many of which orbit very close to their stars. The models also replicate the masses, lifetimes, and...
Before there were galaxies with black holes in their centers, there were vast reservoirs of dark matter coupled to ordinary matter, mostly hydrogen gas. These reservoirs were sprinkled with the Universe’s early stars born in pregalactic dark matter halos. But according to Fellow Mitch Begelman, another population of atypical stars formed millions of years later during the creation of...
The merger of supermassive black holes is a hot topic in astrophysics. Such mergers may occur after the formation of black hole binaries during galaxy collisions. The mergers are predicted to emit gravitational waves, whose detection is the mission of the Laser Interferometer Space Antenna (LISA). In preparation for the LISA mission, which is scheduled for launch in 2018, Fellow Peter Bender...
Most known extrasolar planetary systems comprise planets whose orbits vary wildly from the nearly circular ellipses found in our solar system. This wide variation in eccentricity is thought to occur when large gas planets interact with each other, causing gyrations in planetary orbits, planet migrations toward and away from the central star, and even the ejections of planets out of the star...
Our solar system is currently sprinting around the center of the Milky Way at a speed of 26 km/sec. But, we’re not just hurtling through empty space, according to Fellow Jeff Linsky and former graduate student Seth Redfield (now assistant professor of astronomy at Wesleyan University). We’re surrounded by 15 "nearby" clouds of warm gas, all within 50 light years of the...
Supermassive black holes inside blazar galaxies emit powerful jets of particles traveling in opposite directions near the speed of light. Some are aimed toward the Earth. These jets emit radio waves, which makes them visible to radio telescopes as they streak across the sky. By studying these radio waves, scientists have determined that the jets are traveling at about 99.5% the speed of...
Our comfortably middle-aged Sun completes a rotation once every 28 days. In contrast, young Sun-like stars spin much faster, sometimes whipping around 10 times as quickly. According to widely accepted theory, these young suns build magnetic fields in their convection zones by dynamo processes. Observations of these stars indicate strong magnetic activity. In most stellar dynamo theories,...
The "dark ages" of the early Universe drew to a close with the appearance of enough stars to strip electrons off most of the hydrogen atoms in the gas clouds between galaxies. By a billion years after the Big Bang, these reionized atoms had rendered the Universe transparent to light. About 12.7 billion years later, visiting JILA member Gayler Harford, Fellow Andrew Hamilton, and...
Until recently, astronomers have had difficulty figuring out the composition and size of dust grains in galaxies beyond the Milky Way. They've had some luck with the Large and Small Magellanic Clouds (LMC and SMC, respectively). However, these two "satellite" galaxies are practically our next-door neighbors and much easier to observe.
Now, however, information about...
Astrophysicists know that the centers of galaxies have supermassive black holes whose size correlates with the size of the galaxy surrounding them. They’ve also observed that galaxies collide and merge. In fact, galactic mergers were even more common billions of years ago in the Universe when today’s galaxies were still being assembled.
So what happens to the original...
Take a ride on the Black Hole Flight Simulator, courtesy of Professor Andrew Hamilton. You can read about this work in this NY Times article... http://www.nytimes.com/2006/02/28/science/28prof.html?_r=0
Like people, planets can migrate far from where they were born. In the case of planets, they usually travel toward their parent star, but some may also move away. Some wind up in blistering proximity to their Sun-like parents, orbiting them in 1.2 to 8 days. Such orbits are well inside the magnetic-field-induced cavities that typically separate such stars from their planet-forming accretion...
Graduate student Robyn Levine, Fellow Andrew Hamilton, and colleagues from the University of Chicago’s Kavli Institute for Cosmological Physics are working on modeling how supermassive black holes grow inside galaxies. They recently published the first of what will be a series of papers on a unique cosmological simulation of the growth and evolution of a disk galaxy. What’s unusual about this...
Fellow Phil Armitage is excited about the discovery of several new galaxies in which a disk of water masers is orbiting within half a light year of the central massive black hole. Like their counterpart M106 (NGC 4258) discovered in 1995, these hot (600 K) water molecules mase, i.e., emit coherent radio wavelength photons when they return to lower energy states after being excited by...
What did Fellow Jeff Linsky come home with from a 2006 SINS conference?
He arrived at JILA with the realization that quasars twinkle for much the same reason stars twinkle: Light from both quasars and stars pass through turbulence that mixes up the light rays, causing the light to vary in intensity, or twinkle. However, the stars we see every night twinkle because of turbulence in...
Neutron stars are born in supernovae, spinning very fast. How fast they spin at birth depends on a variety of factors including the initial rotation of the star that goes supernova and what takes place during the supernova explosion. So, if you want to understand these phenomena, one place to start is by investigating how fast a new neutron star can initially spin.
Fellow Rosalba Perna...
Fellow Andrew Hamilton recently confirmed a prediction he made 10 years ago of the location of a reverse shock wave slowing the expansion of the debris from a supernova that occurred in 1006 AD. SN1006 was (and still is) the brightest supernova observed in recorded history; it was visible from Earth (without telescopes) for three years.
This particular stellar cataclysm resulted...
In Ray Bradbury’s book Something Wicked This Way Comes, people get older or younger depending on which direction they ride on a carnival carousel. Something similar may happen to black holes, except that they become gargantuan or just a smidgeon larger depending on how fast they spin while they’re sucking in matter. The slower they spin, the faster they expand, says Visiting...
Two egg-shaped necklaces of magnificent stars orbit the enormous black hole known as Sagittarius A* (Sgr A*) at the center of the Milky Way Galaxy. Sgr A* (shown right) has long been thought to be well past promoting new star formation; until the necklaces were discovered, the black hole was considered to be just an aging, depleted relic of its glory days of organizing the Galaxy.
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There’s a new aspect to research on gamma-ray bursts: their use to discern features of the environment around the star that produced them during its core’s collapse into a black hole. This type of analysis is possible because the spectrum of a gamma-ray burst afterglow is a straight-line continuum without features. Absorption lines can appear in the spectrum because of the...
If you wanted to see a new planet forming, the first thing you'd think of is looking in an accretion disk with a star forming in its center. The problem is it's virtually impossible to actually see a nascent planet inside a swirling, turbulent, and opaque disk of gas and dust. It's much easier to identify planets orbiting stars a billion years old (or older) whose accretion disks...
Our Sun and its eight planets were born in a rough neighborhood nearly 5 billion years ago. Since then our star has traveled countless light years through the Milky Way, and our planet Earth has evolved the only intelligent life we know of in the Universe. Now, Earth's progeny are seeking to understand not only their own origins, but those of the Sun and its planets. They've...
There is an enormous black hole at the center of every galaxy, gobbling up matter over eons of time - some for as long as 13 billion years. One of the great questions of modern astronomy is: Where did the seeds for all these black holes come from? Not, as you might think, from the fiery collapse of massive hot stars formed in the early Universe, says Fellow Mitch Begelman. That may well be...
Juri Toomre and his group concentrate their stellar research close to home – just 93 million miles away, to be precise. They want to answer the question: What dynamic processes occur deep within the Sun? To find out, they use a powerful combination of computer simulations and helioseismology (which analyzes sound waves produced by the Sun to probe its internal structure.) The...
Gamma-ray bursts signal the birth of a new black hole, whether it's created during the collapse of a massive star or via a merger between two compact objects such as neutron stars. Astrophysicists have determined that long gamma-ray bursts are associated with collapsing stars and short bursts are associated with binary mergers. In both cases, however, black-hole accretion powers the...
Galaxy clusters contain enormous clouds of gas whose cooling should result in the formation of a multitude of new stars. But that's not what NASA's Chandra X-ray Observatory is detecting. Instead there's a whole lot less gas cooling and new star formation than scientists had predicted. Perhaps the most mysterious discovery of all is that the clusters are humming – a low B-...
Black holes are pretty strange, sucking in not only nearby matter but also the space around it. These cosmic vacuum cleaners are powered by thin, gaseous accretion disks in orbit around them. Something drives the orbiting gas to spiral in toward the black hole, where all trace of it disappears forever into the singularity. One of the exciting challenges in astrophysics is to figure out the...
We know a lot about cool stars because our Sun is one of them. However, we can't know for sure if cool stars produce winds (like the Sun does) without looking for evidence of such winds. Where stellar winds exist, they interact with hydrogen in the interstellar medium far from the star to produce tell-tale absorption in stellar ultraviolet spectral lines. The solar wind produces a...
Scientists believe that planetary systems coalesce from disks of gas and dust orbiting a star. Similarly, stars can form within massive accretion disks orbiting a black hole. Determining the mechanisms that create stars and planets from these orbiting disks is a hot topic among astrophysicists, according to JILA Fellow Phil Armitage and colleagues W. K. M. Rice of the University of...
Giant gas planets don't often stay in orbit where they're formed. They often move closer to their star or, occasionally, further away. Seldom do they remain in almost circular orbits such as those of Jupiter and Saturn. In fact, all but one of the giant gas planets discovered around other stars are closer to their star than Jupiter is to the Sun. A fraction of these planets are even...
Gamma-ray jets produced deep within massive stars can blow apart the star when they emerge, creating a supernova. The jets are very light and travel near the speed of light toward the star's surface. They are created by a complex interaction of a black hole, an accretion disk, and very strong magnetic fields that come into being when a massive star depletes its supply of hydrogen fuel...
For nearly 18 years, JILA Fellow Dick McCray has been studying the brightest supernova to light up Earth's night skies since the Renaissance. Known as 1987A because it appeared in the southern sky on February 23, 1987, the supernova occurred when a 10-million-year-old blue supergiant star exploded in the Large Magellanic Cloud, a galaxy located 160,000 light years from Earth.
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Rosalba Perna and colleagues Jonathan Granot of Stanford and Enrico Ramirez-Ruiz of Princeton's Institute for Advanced Study recently figured out the relationship between X-ray flashes, X-ray rich gamma-ray bursts, and gamma-ray bursts detected by different space-based observatories. X-ray flashes are transient astronomical X-ray sources that last from several seconds to a few minutes....
What really happens inside black holes?
Andrew Hamilton and Scott Pollack, a graduate student in the Physics Department, recently decided to investigate the answer to this question. In the process, they developed a model using realistic physics that they believe better describes the internal structure of black holes.
The starting point for most black hole models has been...
Andrew Hamilton and Jason Lisle, who received his Ph.D. in astrophysical and planetary sciences in 2004, have proposed a new model for the flow of matter into stationary and rotating black holes. In their "river model of black holes," space flows like a river through a flat background, while objects (like light rays) that move through the river abide by the rules of special...
Left to their own devices, deuterium atoms would attach themselves to cold specks of soot floating in interstellar gas clouds and remain there for eternity. In fact, deuterium has a great affinity for the buckyballs, bucky onions, bucky tubes, and other forms of carbon, such as polycyclic aromatic hydrocarbons, comprising soot. It readily replaces hydrogen in these molecules. Deuterium atoms...
