Astronomers use gamma-ray burst to probe star formation in the early universe

January 07, 2009

LONG BEACH, CA--The brilliant afterglow of a powerful gamma-ray burst (GRB) has enabled astronomers to probe the star-forming environment of a distant galaxy, resulting in the first detection of molecular gas in a GRB host galaxy. By analyzing the spectrum of light emitted in the GRB afterglow, the researchers are gleaning insights into an active stellar nursery in a galaxy so far away it appears as it was 10 billion years ago.

"This observation required a rare and exceptionally bright event to allow us to probe the fragile environment where stars were forming just 3 billion years after the Big Bang. After correcting for the extreme dust extinction, this is intrinsically the second brightest GRB afterglow to date; it would have been easily observed with amateur telescopes, if not for the dust in the way," said Jason X. Prochaska, professor of astronomy and astrophysics at the University of California, Santa Cruz.

Prochaska's team will present its findings at the American Astronomical Society meeting this week in Long Beach, Calif. A paper describing the results has been accepted for publication in Astrophysical Journal Letters.

Stars form in vast clouds of molecular gas and dust, and astronomers have expected to find evidence of these molecular clouds in GRB host galaxies. Until now, however, efforts to detect molecular gas in GRB afterglow spectra had been unsuccessful. The new observations by Prochaska and his coauthors indicate that star formation in the early universe occurred in environments similar to star-forming regions in the Milky Way.

The study focused on a "long duration" gamma-ray burst known as GRB 080607. This type of burst is thought to occur when a massive star collapses to form a black hole. The initial burst of high-energy gamma rays was followed by a slowly fading afterglow of radiation over the entire spectrum of wavelengths.

"We suspect that previous events like 080607 were too faint to be observed on Earth," said coauthor Yaron Sheffer of the University of Toledo. "Many so-called dark bursts, with no observable afterglow, probably mark the dusty, highly extinguished environments of young star-forming regions."

NASA's Swift satellite detected the gamma-ray burst and began x-ray observations, while alerting astronomers and triggering automatic observations by ground-based telescopes such as the Katzman Automatic Imaging Telescope at Lick Observatory. Team members Joshua Bloom, Daniel Perley, and Adam Miller of UC Berkeley happened to be using the Keck I Telescope at the W. M. Keck Observatory in Hawaii and began spectroscopic observations within 15 minutes using the Low Resolution Imaging Spectrograph (LRIS).

The resulting spectrum of the optical afterglow yielded information about the dust, gas, and metals in the interstellar medium through which the light passed on its way out of the host galaxy. In addition to the first clear detection of molecular gases (both carbon monoxide and hydrogen), the spectrum indicated a metal composition comparable to that of the Sun (to astronomers, "metals" are elements heavier than hydrogen and helium).

The spectrum also has many features researchers have never seen before, Prochaska said. In addition to hundreds of standard absorption lines corresponding to known transitions of various elements, the spectrum shows many absorption lines that researchers have yet to identify.

"This is easily the most fascinating spectrum that I've ever worked on," Prochaska said. "Nearly half of the features remain a mystery, and it is possible that no one has ever detected them previously, either in controlled laboratory experiments or in spectra from our galaxy or other galaxies."

There is also more hydrogen in this spectrum than along any path through the Milky Way, he added. "This remains a bit of a puzzle," Prochaska said. "For now, we don't know much about the galaxy that hosted the explosion, but the evidence suggests it has been prodigious in terms of star formation."

The burst and its afterglow were observed in June, and the team did not manage to get images of the host galaxy before it moved to a position in the sky where it could not be observed. In January, the researchers will image the galaxy to connect their findings on the star-forming region with its global properties.

University of California - Santa Cruz

What Are Gamma-Ray Bursts? (Princeton Frontiers in Physics)
by Joshua S. Bloom (Author)

Gamma-ray bursts are the brightest--and, until recently, among the least understood--cosmic events in the universe. Discovered by chance during the cold war, these evanescent high-energy explosions confounded astronomers for decades. But a rapid series of startling breakthroughs beginning in 1997 revealed that the majority of gamma-ray bursts are caused by the explosions of young and massive stars in the vast star-forming cauldrons of distant galaxies. New findings also point to very different origins for some events, serving to complicate but enrich our understanding of the exotic and violent universe. What Are Gamma-Ray Bursts? is a succinct introduction to this fast-growing subject, written by an astrophysicist who is at the forefront of today's research into these incredible cosmic...

Exploding Superstars: Understanding Supernovae and Gamma-Ray Bursts (Springer Praxis Books / Popular Astronomy)
by Alain Mazure (Author), Stéphane Basa (Author)

The exceptional cosmic history and the fabulous destinies of exploding stars – supernovae and gamma-ray bursters – are highly fertile areas of research and are also very special tools to further our understanding of the universe. In this book, cosmologists Dr Alain Mazure and Dr Stéphane Basa throw light on the assemblage of facts, hypotheses and cosmological conclusions and show how these ‘beacons’ illuminate their immediate surroundings and allow us to study the vast cosmos, like searchlights revealing the matter comprising our universe.

Gravitational Radiation, Luminous Black Holes and Gamma-Ray Burst Supernovae
by Maurice H. P. M. van Putten (Author)

Black holes and gravitational radiation are two of the most dramatic predictions of general relativity. The quest for rotating black holes - discovered by Roy P. Kerr as exact solutions to the Einstein equations - is one of the most exciting challenges facing physicists and astronomers. Gravitational Radiation, Luminous Black Holes and Gamma-Ray Burst Supernovae takes the reader through the theory of gravitational radiation and rotating black holes, and the phenomenology of GRB-supernovae. Topics covered include Kerr black holes and the frame-dragging of spacetime, luminous black holes, compact tori around black holes, and black-hole spin interactions. It concludes with a discussion of prospects for gravitational-wave detections of a long-duration burst in gravitational-waves as a method...

Gamma-Ray Bursts: The brightest explosions in the Universe (Springer Praxis Books / Astronomy and Planetary Sciences)
by Gilbert Vedrenne (Author), Jean-Luc Atteia (Author)

Since their discovery was first announced in 1973, gamma-ray bursts (GRBs) have been among the most fascination objects in the universe. While the initial mystery has gone, the fascination continues, sustained by the close connection linking GRBs with some of the most fundamental topics in modern astrophysics and cosmology. Both authors have been active in GRB observations for over two decades and have produced an outstanding account on both the history and the perspectives of GRB research.

The Biggest Bangs: The Mystery of Gamma-ray Bursts, the Most Violent Explosions in the Universe
by Jonathan I. Katz (Author)

Gamma-ray bursts are the most violent events since the birth of the universe. They are about ten times more energetic than the most powerful supernovae. At their peak, gamma-ray bursts are the brightest objects in space, about 100,000 times brighter than an entire galaxy. And yet until recently these titanic eruptions were the most mysterious events in astronomy.
In The Biggest Bangs, astrophysicist Jonathan Katz offers a fascinating account of the scientific quest to unravel the mystery of these incredible phenomena. With an eye for colorful detail and a talent for translating scientific jargon into plain English, Katz ranges from the accidental discovery of gamma-ray bursts (by a Cold War satellite system monitoring the Nuclear Test Ban Treaty) to the frustrating but ultimately...

Cosmic Explosions in Three Dimensions: Asymmetries in Supernovae and Gamma-Ray Bursts (Cambridge Contemporary Astrophysics)
by Peter Höflich (Editor), Pawan Kumar (Editor), J. Craig Wheeler (Editor)

Recent observations have demonstrated that supernovae and gamma ray bursts are driven by strong jets of energy and other asymmetrical effects that reveal unknown physical properties. This volume highlights the burgeoning era of routine supernova polarimetry and the new insights into core collapse and thermonuclear explosions. Chapters by leading scientists summarize the status of a rapidly developing perspective on stellar explosions in a valuable resource for graduate students and research scientists.

Deciphering the Ancient Universe with Gamma-Ray Bursts (AIP Conference Proceedings / Astronomy and Astrophysics)
by Nobuyuki Kawai (Editor), Shigehiro Nagataki (Editor)

Gamma-ray bursts (GRBs) are the most luminous and violent explosions detectable out to the edge of the observable Universe. As soon as their cosmological origin was established, it became apparent that GRBs can serve as powerful probes of the high-redshift Universe. The association of long GRBs with the deaths of massive stars imply that they trace the sites and history of massive star formation. Their optical and near-infrared afterglows reveal spectral imprints of their environments, including the interstellar medium of their host galaxies as well as the intergalactic medium during cosmic reionization. With the Swift Observatory in orbit, such expectations are now being materialized. With GRB 050904, we found that the Universe was already largely ionized at z=6.3. The discovery of GRB...

Toward an Understanding of the Progenitors of Gamma-Ray Bursts
by Joshua S. Bloom (Author)

The various possibilities for the origin ("progenitors") of gamma-ray bursts (GRBs) manifest in differing observable properties. Through deep spectroscopic and high-resolution imaging observations of some GRB hosts, I demonstrate that well-localized long-duration GRBs are connected with otherwise normal star-forming galaxies at moderate redshifts of order unity. Using high-mass binary stellar population synthesis models, I quantify the expected spatial extent around galaxies of coalescing neutron stars, one of the leading contenders for GRB progenitors. I then test this scenario by examining the offset distribution of GRBs about their apparent hosts making extensive use of ground-based optical data from Keck and Palomar and space-based imaging from the Hubble Space Telescope. The offset...

Gamma-Ray Bursts: 30 Years of Discovery: Gamma-Ray Burst Symposium (AIP Conference Proceedings / Astronomy and Astrophysics)
by E.E. Fenimore (Editor), M. Galassi (Editor)

In the last thirty years, gamma-ray bursts have grown from an oddity to a central position in astrophysics. Not only are they the largest explosions since the big bang, capable of flooding most of the universe with gamma-rays, but their brilliance serves as a backlight that can illuminate the cosmos far deeper into the early universe than any other object. Their unpredictability has forced researchers to use extreme measures to observe them: completely autonomous satellites and robotic ground-based telescopes. Their bizarre physical properties have pushed us to develop new theories of astrophysical explosions. Topics include: global properties of GRBs; X-ray flashes; ultra-high energy gamma-rays, neutrinos, gravity waves; prompt emission and early afterglows; relativistic jets and...

Gamma-Ray Bursts 2007: Proceedings of the Santa Fe Conference (AIP Conference Proceedings / Astronomy and Astrophysics)
by Mark Galassi (Editor), David Palmer (Editor), Edward Fenimore (Editor)

For more than three decades, gamma-ray bursts have grown from an oddity to a central topic in astrophysics. Not only are they the largest explosions since the big bang, capable of flooding most of the universe with gamma-rays, but their brilliance serves as a backlight that can illuminate the cosmos far deeper into the early universe than any other object. Their unpredictability has forced researchers to use extreme measures to observe them: completely autonomous satellites and robotic ground-based telescopes. Their bizarre physical properties have required new theories on massive explosions.