Farewell to the standard candles

One gamma-ray flash in space is not like another

When the universe is briefly illuminated by a gigantic flash, a star in a distant galaxy probably dies and a black hole is born. Immense amounts of energy are released and permeate the universe. Until now, astronomers believed that these gamma-ray flashes always released the same amount of gamma rays, but according to new research, they are not all so-called "standard candles", but coarser and smaller lights.

Nothing releases as much energy abruptly in space as a gamma ray burst (grb). The phenomenon was accidentally discovered by russian and american spy satellites in 1968. While searching for traces of above-ground nuclear weapons testing, the instruments detected a brief, very intense burst of gamma rays from deep space. Seven years ago, the origin of such a burst was located in a remote galaxy.

Surprise in cosmic proximity

Cosmic gamma-ray bursts last only a very short time, ranging from less than a second to several minutes. Astrophysicists ame that a large part of them is produced by the collapse of a dying star into a black hole. The hot gas disk around the all-grinding hole (hot secrets of the black monster) produces huge amounts of energy and blows it into space as a very energetic jet along the rotation axis of the dying star. Extremely intense gamma ray flashes shine from all directions of space, they are the most powerful explosions in the universe.

Farewell to the standard candles

The artistic conception of gamma ray flashes

So far, so good. Now, however, two groups of researchers present their analyses in the scientific journal nature, which prove that not all gamma ray flashes have the same strong energy. Sergey sazonov and colleagues from the max planck institute for astrophysics in garching, germany, and alicia soderberg and colleagues from caltech optical observatories and five other institutes in the u.S., have taken a closer look at grb 031203, which – like all grbs – was identified by its discovery date of 3. December 2003 was named. The european gamma-ray observatory integral had tracked it and observed it. With a total length of 40 seconds grb 031203 belongs to the long lasting and since it was observed from a distance of "only" 1.3 billion light-years away, one of the most earth-dark gamma-ray bursts ever sighted.

Two weak brothers

Immediately after its discovery, an armada of observatories on earth and in orbit aligned themselves with grb 031203. At first it seemed to behave according to expectations. Like all other gamma ray bursts it became fainter and fainter with time, its energy was distributed on different wavelengths. But it did not come from the other end of the universe and in fact it faded considerably. Sergey sazonov explains:

Because it was so close, grb 031203 should actually appear very bright, but its energy in gamma rays, according to quantities of "integral" about a thousand times lower than we normally expect from a gamma-ray burst. The idea that all gamma-ray bursts release the same amount of gamma radiation, or, as we say "standard candles" is disproved by the new observations.

It reminded researchers, including soderberg’s group, who analyzed the afterglow of grb 031203, of another gamma-ray flash discovered back in 1998. The afterglow occurs when the explosion wave of the gamma-ray flash heats up the evaporated gas in the vicinity of the flash source and it remains observable for weeks or months while it becomes weaker and weaker. Grb 980425 occurred at a distance of only 130 million light years and was ten thousand times fainter than a typical gamma-ray burst. However, some scientists also doubted whether it was a true grb.

Fast, luminous and full of energy

Gamma-ray flashes light up so briefly that for a long time it was difficult to locate and determine them precisely. Only the latest generation of instruments makes this possible. The fact that so far almost only cosmic flashes with similar energy signatures have been detected may also be due to technology. Very distant, weak flashes remain invisible for us so far, because the sensitivities of the devices are not high enough.

Farewell to the standard candles

Sky region around the gamma-ray burst grb 031203, imaged with the ibis instrument of the "integral"-satellite in the rontgen beam energy range between 17 and 50 kev. The gamma-ray burst was detectable for about 40 seconds, during which time it far outshone the neighboring rontgen sources vela x-1 and mx 0836-429 (marked by crosses).

The observations of the brightness in the rontgen light in the afterglow showed clearly that this radiation was also correspondingly weaker at grb 031203, likewise in the radio wave range. The researchers ame that probably a whole population of low-energy gamma-ray bursts has escaped observation so far. Nasa’s swift gamma-ray burst mission, scheduled to launch in october, could shed light on the subject and discover even distant faint gamma-ray bursts in deep space.