Extreme Universe
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Skobeltsyn Institute of Nuclear Physics of Moscow State University Skobeltsyn Institute of Nuclear Physics of Moscow State University
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Outstanding Problems of Extreme Universe Astrophysics

  1. Seeking for the Most Distant Objects in the Universe...
  2. Measuring the Early Universe and First Stars with Gamma-Ray Bursts.
1. Seeking for the most distant objects in the Universe.

Fig.1. The Most Distant Object Yet Discovered in the Universe | ESO's Very Large Telescope has shown that a faint gamma-ray burst detected last Thursday is the signature of the explosion of the earliest, most distant known object in the Universe (a redshift of 8.2). The explosion apparently took place more than 13 billion years.

GAMMA RAY BURSTS ARE AMONG THE MOST DISTANT OBJECTS IN THE UNIVERSE

GRB and faint galaxy images have been competing over the last few years for the title of the most distant object in the universe. They are the universe’s most luminous explosions. Most occur when massive stars run out of nuclear fuel. As their cores collapse into a black hole or neutron star, gas jets punch through the star and blast into space. — driven by processes not fully understood — There, they strike gas previously shed by the star and heat it, which generates short-lived afterglows in many wavelengths As they are also the brightest luminous source of the electromagnetic radiation in the Universe, detection of them can provide the discovery of most young gravitationally bounded object in the Universe.

The most distant GRB every discovered, GRB 090429B occurred in April of 2009, with a red shift of 9.4 or a distance of roughly 323 billion light years from earth. We are looking at an event that occurred when the universe was only about 1/2 billion years old, or at a time when the universe was only about 1/26 it’s present age. This is just getting started, however GRB can be detected to red shifts of 14 or more!

As the first we talking about Long GRBs, which physically connected with first massive star collapse in the Universe. The possible mass is about more then 30-100 solar mass with thermonuclear evolution time several million years. For example the typical age of the Universe is about:

T = 2/(3H) (1+z)(-3/2) ~ 7 106 (Z/100)(-3/2) yrs

The time is more than enough. But really the first stars formation connected with formation of the nonlinear gravitational perturbations. The more realistic (including CMB data) estimations give maximal red shift is about 12 or slightly more. For example, the discovery GRB at z>15 is means a new problems for standard cosmological model.

The Lyman continuum (912A) comes to infrared diapason to more 10000 A for z>10. The shorter ultraviolet quanta is absorbed. So Infra Red receiver is extremely needed!

2. Measuring the Early Universe and First Stars with Gamma-Ray Bursts.
Fig.2. Gamma-ray bursts (GRBs) are short (a few milliseconds to several minutes), very intense flashes of gamma-rays associated with stellar scale events at cosmological distances.

 

GRB SHINE A SPOTLIGHT ON THE PROCESSES OF THE EARLY UNIVERSE!

The most distant galaxies measured are typically the faintest detectable objects in very long exposures. GRB are different; GRB are bright, even the most distant ones. They are often bright enough for spectroscopic measurements. Material in the deepest, most distant voids of space, normally hidden from our view, can be studied as it absorbs the light from the GRB at specific wavelengths, like an intruder leaving a fingerprint in the GRB spectrum. The GRB itself tells us where early star formation — possibly the first stars — has occurred; the spectrum can tell us about anything else in between the GRB and our earth.

Fig. 3. This artist's impression shows two galaxies in the early universe. The brilliant explosion on the left is a gamma-ray burst. The light from the burst travels through both galaxies on its way to Earth (outside the frame to the right). Analysis of observations of the light from this gamma-ray burst made using ESO's Very Large Telescope have shown that these two galaxies are remarkably rich in heavier chemical elements. Credit: ESO/L. Calcada

Gamma-ray bursts are the brightest explosions in the Universe. They are first spotted by orbiting observatories that detect the initial short burst of gamma rays. After their positions have been pinned down, they are then immediately studied using large ground-based telescopes that can detect the visible-light and infrared afterglows that the bursts emit over the succeeding hours and days. One such burst, called GRB 090323, was first spotted by the NASA Fermi Gamma-ray Space Telescope. Very soon afterwards it was picked up by the X-ray detector on NASA’s Swift satellite and with the GROND system at the MPG/ESO 2.2-metre telescope in Chile and then studied in great detail using ESO’s Very Large Telescope (VLT) just one day after it exploded.

The VLT observations show that the brilliant light from the gamma-ray burst had passed through its own host galaxy and another galaxy nearby. These galaxies are being seen as they were about 12 billion years ago. Such distant galaxies are very rarely caught in the glare of a gamma-ray burst.

«When we studied the light from this gamma-ray burst we didn’t know what we might find. It was a surprise that the cool gas in these two galaxies in the early Universe proved to have such an unexpected chemical make-up,» explains Sandra Savaglio (Max-Planck Institute for Extraterrestrial Physics, Garching, Germany), lead author of the paper describing the new results. «These galaxies have more heavy elements than have ever been seen in a galaxy so early in the evolution of the Universe. We didn’t expect the Universe to be so mature, so chemically evolved, so early on.»

As light from the gamma-ray burst passed through the galaxies, the gas there acted like a filter, and absorbed some of the light from the gamma-ray burst at certain wavelengths. Without the gamma-ray burst these faint galaxies would be invisible. By carefully analysing the tell-tale fingerprints from different chemical elements the team was able to work out the composition of the cool gas in these very distant galaxies, and in particular how rich they were in heavy elements.

Fig. 4. GRB 080607 is the first gamma-ray burst to show molecules in its afterglow spectrum. It offers a first glimpse into the star-forming region of a galaxy from the early universe

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 11.5 billion years ago.

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.

This observation required a rare and exceptionally bright event to allow us to probe the fragile environment where stars were forming just 2.2 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.

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.

Based on their prompt emission properties, GRBs are divided in long/soft and short/hard bursts. The short GRB has a typical duration less than 4 sec and more hard spectrum than long GRB. Due to their short duration there are no optical prompt observations of short GRB up to now...

The SHOK experiment on Lomonosov will be the first Very Wide Filed (2000 square degrees) optical experiment in space.

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Skobeltsyn Institute of Nuclear Physics of Moscow State University
Lomonosov Moscow State University Skobeltsyn Institute of Nuclear Physics (MSU SINP),
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