Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A simple survey yields a cosmic conundrum

02.08.2006
A survey of galaxies observed along the sightlines to quasars and gamma-ray bursts--both extremely luminous, distant objects--has revealed a puzzling inconsistency. Galaxies appear to be four times more common in the direction of gamma-ray bursts than in the direction of quasars.

Quasars are thought to be powered by accretion of material onto supermassive black holes in the centers of distant galaxies. Gamma-ray bursts, the death throes of massive stars, are the most energetic explosions in the universe. But there is no reason to expect galaxies in the foreground to have any association with these background light sources.

"The result contradicts our basic concepts of cosmology, and we are struggling to explain it," said Jason X. Prochaska, associate professor of astronomy and astrophysics at the University of California, Santa Cruz.

Prochaska and graduate student Gabriel Prochter led the survey, which used data from NASA's Swift satellite to obtain observations of the transient, bright afterglows of long-duration gamma-ray bursts (GRBs). They described their findings in a paper accepted for publication in Astrophysical Journal Letters. The paper, which could have strange cosmological implications, has been a source of significant debate among astronomers throughout the world.

The study is based on a fairly straightforward concept. When light from a GRB or a quasar passes through a foreground galaxy, the absorption of certain wavelengths of light by gas associated with the galaxy creates a characteristic signature in the spectrum of light from the distant object. This provides a marker for the presence of a galaxy in front of the object, even if the galaxy itself is too faint to observe directly.

Prochter and Prochaska analyzed 15 GRBs in the new study and found strong absorption signatures indicating the presence of galaxies along 14 GRB sightlines. They had previously used data from the Sloan Digital Sky Survey (SDSS) to determine the incidence of galaxies along the sightlines to quasars. Based on the quasar study, they would have predicted only 3.8 galaxies instead of the 14 detected along the GRB sightlines.

The quasar analysis was based on more than 50,000 SDSS observations, so the data for quasars are much more robust statistically than the data for GRBs, Prochaska said. Nevertheless, the probability that their results are just a statistical fluke is less than about one in 10,000, he said.

The researchers examined three potential explanations for the inconsistency. The first is obscuration of some quasars by dust in galaxies. The idea is that if a quasar is behind a dusty galaxy it wouldn't be seen, and this could skew the results. "The counter argument is that with this huge database of quasar observations, the effect of dust has been well characterized and it should be minimal," Prochter said.

Another possibility is that the absorption lines in the GRB spectra are from gas ejected by the GRBs themselves, rather than from gas in intervening galaxies. But in nearly every case when researchers have taken a closer look in the direction of the GRB, they have in fact found a galaxy at the same position as the gas.

The third idea is that the intervening galaxy may act as a gravitational lens, enhancing the brightness of the background object, and that this effect is somehow different for GRBs than for quasars. Although Prochaska said he prefers this explanation, several factors make strong lensing of the GRBs seem unlikely.

"Those who know more about gravitational lensing than I do tell me it's unlikely to be the answer," Prochaska said.

The paper, a draft of which has been posted on an Internet server for several weeks, has stimulated widespread discussion and at least one new paper proposing a potential explanation. But so far the findings remain perplexing.

"A lot of people have been scratching their heads, and most hope that it goes away," Prochaska said. "The GRB sample is small, so we would like to triple or quadruple the number in our analysis. That should happen during Swift's extended mission, but it will take time."

Tim Stephens | EurekAlert!
Further information:
http://www.ucsc.edu

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>