Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Leading theories of cosmic explosions contradicted in a flash

01.06.2005


Satellite that could help solve mystery to be deactivated in September

Observations of a cosmic explosion detected on Feb. 15 by two NASA satellites have thrown into doubt one popular explanation for such explosions and have also seriously weakened the argument for yet another, according to University of Chicago astrophysicist Don Lamb. But solving the mystery any time soon may be forestalled by plans to shut down one of the satellites in September.

The explosion in question is a powerful burst of X-rays called an X-ray flash that was observed by NASA’s Swift and High Energy Transient Explorer-2 satellites. X-ray flashes seem to be related to gamma-ray bursts, the most powerful explosions in the universe. "No one understands this relationship at all. It’s a complete mystery," said Lamb, the Louis Block Professor in Astronomy & Astrophysics at the University of Chicago and a member of the HETE-2 science team.



Lamb will present some ideas on the relationship of X-ray flashes to gamma-ray bursts on May 31 during a meeting of the American Astronomical Society in Minneapolis. The co-authors of his paper are Tim Donaghy, a Ph.D. student in physics, and Carlo Graziani, Senior Research Associate in Astronomy & Astrophysics, both at the University of Chicago.

Discovered in 1969, Gamma-ray bursts last anywhere from fractions of a second to many minutes and pack the output of as many as 1,000 exploding stars. They occur almost daily, come from any direction in the sky, and are followed by afterglows that are visible for a few days at X-ray and optical wavelengths.

Discovered in 2000, X-ray flashes seem to form the less powerful end of a continuum of cosmic explosions that progresses to X-ray rich gamma-ray bursts and then culminates in gamma-ray bursts proper. All three phenomena occur in approximately equal numbers.

"We think that regular gamma-ray bursts are all produced by the collapse of massive stars and probably the creation of black holes," Lamb said. "I personally think it’s essentially a certainty that X-ray flashes are produced by the same kind of event."

But exactly how that occurs remains a matter of speculation. One possibility is that a varying rotation rate of the collapsed core of these massive stars produces different opening angles of the jets emitted from the bursts. "Maybe sometimes they’re rotating rapidly and you get narrow jets and other times they’re rotating less rapidly and you get wider X-ray rich jets and sometimes they’re rotating still more slowly and you get very broad jets that produce the X-ray flashes," Lamb explained.

The Feb. 15 X-ray flash, designated XRF 050215b, has yielded the best data ever on this phenomenon, thanks to the joint observations of the two NASA satellites. The next-best data come from a flash known as XRF 020427, detected in April 2002 by the Italian BeppoSAX satellite. Three characteristics of both flashes conflict with a popular theory that X-ray flashes are gamma-ray bursts as viewed from slightly off to the side of the jet instead of head on.

First, according to the popular theory, scientists expected the energy levels of an X-ray flash’s afterglow to connect smoothly on a gradient with the energy of the burst itself. Second, they expected the afterglow to fade fast. And third, they expected the afterglow to be faint when compared to the original burst.

These expectations all follow from Albert Einstein’s theory of special relativity, but none of them have panned out. Scientists apparently cannot rely on special relativity to explain X-ray flashes, Lamb said.

The satellite observations also conflict with the theory that the shape of the jets from a gamma-ray burst are universal, but only look different because of the viewing angle. Based on this theory, scientists would have predicted that the afterglow of the Feb. 15 X-ray flash afterglow would have faded within a day or so following the initial burst. But the afterglow showed now signs of fading even five days following the burst.

One theory suggests that all three types of explosions contain the same amount of energy, but that the opening angle of the jet emitted from the explosions defines their apparent brightness. In this scenario, narrow jets produce the gamma-ray bursts, wider jets result in X-ray rich gamma-ray bursts, and the broadest lead to X-ray flashes. Lamb and many others view this theory as a possibility. "There’s a lot of people who don’t or are not at all sure," he said.

The question could probably be settled within the next few years with more burst observations conducted jointly between the Swift and HETE-2 satellites, which measure slightly different properties of the phenomena. But NASA plans to discontinue the HETE-2 mission this September.

NASA would somehow need to find an additional $1.5 million annually to keep HETE-2 operating. "It’s not the best budgetary climate to try to pull this thing off," Lamb said. But if NASA somehow manages to do it, "The HETE mission would leverage the science that Swift could do by a significant amount," he said.

Steve Koppes | EurekAlert!
Further information:
http://www.uchicago.edu

More articles from Physics and Astronomy:

nachricht Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

NTU scientists build new ultrasound device using 3-D printing technology

07.12.2016 | Health and Medicine

The balancing act: An enzyme that links endocytosis to membrane recycling

07.12.2016 | Life Sciences

How to turn white fat brown

07.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>