All high energy astrophysics stories

'Wintering-over' at the South Pole

70652986 — Mon, 26 Mar 2007 06:26:25 -0400

They came to the South Pole, enduring months of bitter cold, darkness, and isolation, to peer at the galaxy's center through clear, dry skies. And in December, they - scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) - declared "mission accomplished."

After 11 years, the Antarctic Submillimeter Telescope and Remote Observatory, AST/RO, was dismantled last fall. The 1.7- meter telescope was boxed up for transport and now sits on the snow, awaiting a decision on its next stop.

Taking a CAT scan of the early universe

70652986 — Mon, 26 Mar 2007 05:36:09 -0400

Reporting in the Nov. 11, 2004, issue of Nature, astrophysicists J. Stuart B. Wyithe (University of Melbourne) and Abraham Loeb (Harvard-Smithsonian Center for Astrophysics) have calculated the size of cosmic structures that will be measured when astronomers effectively take CAT scan-like images of the early universe. Those measurements will show how the universe evolved over its first billion years of existence. "Until now, we've been limited to a single snapshot of the universe's childhood -- the cosmic microwave background," says Loeb. "This new technique will let us view an entire album full of the universe's baby photos. We can watch the universe grow up and mature." The heart of the tomography technique described by Wyithe and Loeb is the study of 21-centimeter-wavelength radiation from neutral hydrogen atoms. In our own galaxy, this radiation has helped astronomers to map the Milky Way's spherical halo. To map the distant young universe, astronomers must detect 21-cm radiation that has been redshifted: stretched to longer wavelengths (and lower frequencies) by the expansion of space itself. "Tomography is a complicated process, which is one reason why it hasn't been done before at very high redshifts," says Wyithe. "But it's also very promising because it's one of the few techniques that will let us study the first billion years of the universe's history."

Young star caught speeding

70652986 — Mon, 26 Mar 2007 05:34:51 -0400

Findings linking a speeding star to its birthplace provide direct observational support of theoretical simulations predicting that protostars can be tossed out of a young cluster. This is the first time that such a fast-moving young star has been seen outside of a cluster or binary system. Astronomers Alyssa Goodman (Harvard-Smithsonian Center for Astrophysics) and Héctor Arce (Caltech) announced Jan. 5, 2004 at the 203rd meeting of the American Astronomical Society that they have caught a newly formed star in the act of speeding. PV Ceph, located about 1,400 light years away in the constellation Cepheus, is whizzing through space at a speed of 40,000 miles per hour-some 40 times faster than a speeding bullet. And like a bullet, it left an exit wound when it ripped out of the star cluster where it formed. The discovery has significant implications for calculations of star formation efficiency -- how many stars of what sizes are likely to form from a given molecular cloud. Modeling that process correctly is critical to understanding how galaxies everywhere turn gas into stars.

Astronomers link gamma-ray bursts, supernovae

70652986 — Mon, 26 Mar 2007 05:29:44 -0400

Gamma-ray bursts are incredibly bright flashes of high-energy radiation that likely signal the birth of black holes. Bursts occur at random locations scattered across the sky, and few last more than a minute, making them a challenge to study. A supernova is the explosion of a star at least eight times as massive as the Sun. When such stars deplete their nuclear fuel, they no longer have the energy to support their mass. Their cores implode, forming either a neutron star or (if there is enough mass) a black hole. Could the two be related? Astronomers didn't know for sure until a recent investigation uncovered the connection. "There should no longer be doubt in anybody's mind that gamma-ray bursts and supernovae are connected," said Thomas Matheson of the Harvard-Smithsonian Center for Astrophysics, a member of the team that made this discovery. The investigation began on March 29, 2003, when NASA's High-Energy Transient Explorer satellite discovered one of the brightest and closest gamma-ray bursts on record. Located in the constellation Leo, the 30-second burst outshone the entire Universe in gamma rays, and its optical afterglow was still over a trillion times brighter than the Sun two hours later. Through observations of that afterglow on subsequent nights, astronomers spotted the telltale signs of a supernova. The team cannot yet determine the timing of the burst relative to the supernova (whether one preceded the other or whether both began at the same time), but the same event - a star explosion - was certainly the trigger for both.

X-ray arcs tell tale of giant eruption

70652986 — Mon, 26 Mar 2007 05:25:27 -0400

Scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) report that two arc-like structures of multimillion-degree gas in the galaxy Centaurus A appear to be part of a ring 25,000 light years in diameter. The size and location of the ring suggest that it could have been produced in a titanic explosion that occurred about 10 million years ago. A composite image of the galaxy made with radio (red and green), optical (yellow-orange), and X-ray data (blue) presents a stunning tableau of a tumultuous galaxy. A broad band of dust and cold gas is bisected at an angle by opposing jets of high-energy particles blasting away from the supermassive black hole in the nucleus. Lying in a plane perpendicular to the jets are the two large arcs of X-ray emitting hot gas.

Astronomers take the measure of dark matter in the universe

70652986 — Mon, 26 Mar 2007 05:15:32 -0400

Astronomers believe that most of the matter in the universe is invisible to us -- so called "dark matter." The nature of this dark matter is not known, but most astronomers think that it is in the form of an as-yet-unknown type of elementary particle that contributes to gravity through its mass but otherwise interacts weakly with normal matter. These dark matter particles are often called WIMPs, an acronym for "weakly interacting massive particles." Using the Chandra X-ray Observatory, a research team observed five galaxy clusters to determine how much dark matter they contain. Galaxy clusters are vast concentrations of galaxies, hot gas and dark matter spanning millions of light years, held together by gravity.

Young pulsar reveals clues to supernova

70652986 — Mon, 26 Mar 2007 05:15:39 -0400

Using the Chandra X-ray Observatory to learn more about pulsars, A team led by Stephen Murray of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., studied 3C58, the remains of a supernova observed on Earth in 1181 AD in the constellation Cassiopeia. 3C58 is one of the youngest known pulsars, and behaves quite differently from the better known pulsar in the Crab Nebula, which is about the same age. The observations of 3C58 will enable scientists to better understand how neutron stars are formed in the seconds just before a supernova explosion, and how they pump energy into the space around them for thousands of years after the explosion. 3C58 is a neutron star rotating 15 times a second, which means it is rotating at about half the rate of the Crab Nebula pulsar.

Astronomers detect dust disks around very young brown dwarfs in the Orion Nebula

70652986 — Mon, 26 Mar 2007 05:13:37 -0400

The results of recent observations by an international team of astronomers suggest that brown dwarfs share a common origin with stars. Brown dwarfs are more similar in nature to stars than to planets and, like stars, have the potential to form with accompanying systems of planets. The observation by the researchers of dusty protoplanetary disks around the faintest objects in the Orion Nebula cluster confirms both the membership of these faint stars in the cluster and their nature as bona fide substellar objects, making this the largest population of brown dwarf objects yet known.

Star factory near galactic center bathed in high-energy X-rays

70652986 — Mon, 26 Mar 2007 05:13:41 -0400

A team of astronomers, including some from the Harvard-Smithsonian Center for Astrophysics, has looked into the core of our own Milky Way galaxy and discovered a new phenomenon. The "cauldron" of 60-million-degree gas surrounding a group of young stars in the Arches Cluster supports earlier theoretical predictions about what happens when solar winds from massive stars collide with each other: they form very hot gas and generate X-rays. The discovery was made by a research team headed by Professor Farhad Zadeh of Northwestern University. The team used NASA's Chandra X-ray Observatory to make its observations. Massive stars, newborn stars, and stellar winds have long been known to emit X-rays.

A quasar's identity may simply be in eye of beholder

70652986 — Mon, 26 Mar 2007 05:13:46 -0400

A quasar is a super-massive black hole; quasars are among the most energetic objects in the Universe. Most quasars are extremely bright in optical light, but about 10 percent of them appear hidden by clouds of gas and dust. Are these 10 percent different from the rest of the quasars?

Dark night sky tells us about structure and formation of solar system

70652986 — Mon, 26 Mar 2007 05:09:27 -0400

The darkness of the night sky is one of astronomy's great puzzles. An infinite universe uniformly filled with stars and galaxies should produce an infinitely bright night sky, Johannes Kepler concluded 400 years ago. So why is the sky dark? It has to do with the finite size of the Milky Way Galaxy and the finite age of an infinite, expanding universe. Now, two astronomers have shown that the dark night sky also tells us about the structure and formation of our solar system. In a paper published in the Astrophysical Journal Letters, Scott J. Kenyon (Smithsonian Astrophysical Observatory) and Rogier A. Windhorst (Arizona State University) have used the dark night sky to set new limits on the amount of material in the outer reaches of the solar system. This observation tells us about how planets like Pluto were formed in our own solar system.

Astronomers resolve visible blast wave from gamma-ray burst

70652986 — Mon, 26 Mar 2007 05:09:29 -0400

Gamma-ray bursts (GRBs) are mysterious flashes of high-energy light that are detected about once a day somewhere in the sky. However, their origin remains unknown to astronomers, most of whom believe GRBs are enormous explosions that occur far across the Universe. Now for the first time, astronomers have resolved the visible blast wave produced by a gamma-ray burst. By taking advantage of a fortuitous cosmic alignment, a team of scientists was able to focus the light from a gamma-ray event halfway across the universe. The researchers were able to achieve this elusive goal: to see the ring-shaped structure caused by the gamma-ray burst because of "gravitational microlensing." Predicted by Einstein's theory of general relativity, microlensing occurs when the light from a very distant source -- in this case, a gamma-ray burst -- is amplified by the gravity of an intervening object.

Mystery of cometary X-rays solved

70652986 — Mon, 26 Mar 2007 05:09:48 -0400

Comets, which resemble "dirty snow balls" a few miles in diameter, until recently were thought to be too cold to emit X-rays. So the detection of X-rays from comet Hyakutake in 1996 was a surprise. Several explanations were suggested, but the source of cometary X-ray emission remained a puzzle. NASA's Chandra X-ray Observatory in July 2000 captured images of Comet C/1999 S4 (LINEAR) and detected X-rays from oxygen and nitrogen ions. The observation showed that they are produced by collisions of ions racing away from the sun with gas in the comet. "This observation solves one mystery. It proves how comets produce X-rays," said Carey Lisse, leader of the scientific team.

Nebula resembles gigantic cosmic crossbow

70652986 — Mon, 26 Mar 2007 05:09:50 -0400

NASA's Chandra X-ray Observatory captured the details of a compact nebula that resembles a gigantic cosmic crossbow. The nebula, located in the Vela supernova remnant, is created as a rapidly rotating neutron star, or pulsar, spins out rings and jets of high energy particles while shooting through space. The X-ray jet can be traced all the way into the neutron star, and an inner ring is seen for the first time. This ring is thought to represent a shock wave due to matter rushing away from the neutron star. More focused flows at the neutron star's polar regions produce jets of particles that blast away at near the speed of light.

South Pole telescope sees origin of starbursts

70652986 — Mon, 26 Mar 2007 05:09:23 -0400

Astronomers have seen how star formation occurs in the center of our own Milky Way Galaxy by using a telescope based at the South Pole. The observations contribute to our knowledge of how stars form in "bursts" near the center of the galaxy at roughly 500-million-year intervals. The scientists were able to show that a ring of material near the galaxy center contains, on average, several thousand molecular hydrogen molecules per cubic centimeter. This density is near a critical value. If the density is below this value, then the ring can persist as a uniform ring of material in orbit around the galactic center. If additional material is added, however, increasing the density, then the ring will come together under its own gravity and form a giant molecular cloud.