1E 0657−558
In the background in the visible spectrum, images recorded by the Magellan telescope and the Hubble space telescope .
The X-ray emission of the intergalactic gas clouds recorded by the Chandra space telescope is superimposed on this in pink and the mass distribution calculated from gravitational lensing effects is superimposed on it.
1E 0657−558 (also known as bullet cluster , German "Geschosshaufen") is a galaxy cluster in the constellation Kiel of the ship . The exact coordinates of the cluster are right ascension 06 h 58 m 29 s and declination -55 ° 57 '. The redshift is z = 0.296. This corresponds to a light transit time of 3.4 billion years, or a moving distance of 3.9 billion light years , because the universe has expanded somewhat during the long light transit time.
Description and meaning
X-ray observations showed that the bullet cluster actually consists of two galaxy clusters. The far more massive of the two is located in the east (left in the picture) and was crossed by the second, smaller one about 100 million years before the observed time. This (in the west or on the right in the picture) appears in the X-ray images like a bullet, hence the name. Both clusters show a significantly increased galaxy density and are observed today at a mutual distance of about 0.72 Mpc . The radial speeds differ only slightly, so that the direction of the collision must have been approximately perpendicular to the visual axis.
Independently of each other, three core variables were examined more closely in the bullet cluster:
- the distribution of galaxies (observations in visible light)
- the distribution of the inter-galactic plasma (red in the image; observations in the X-ray range with the Chandra - Telescopic ) and
- the mass distribution or the gravitational potential (blue in the picture; observations of the gravitational lensing effect on images of the Hubble space telescope ); this effect is quite small and is reflected in a deformation of the images of the background galaxies (a statistical approach must then be made here).
It turned out that the individual components of the galaxy cluster are unusually clearly separated from one another: the distribution of the mass (dark matter) follows the distribution of the galaxies; the intergalactic gas ("bright" baryonic matter ) does not do this, it "lags" behind the bullet cluster. This observation provides a further indication of the existence of dark matter and makes 1E 0657−558 an important object for research.
However, a later study (2010) found that the speed of the colliding galaxy cluster was inconsistent with the predictions of the Lambda CDM model .
Explanation
Binding mechanism of galaxy clusters
Galaxy clusters are collections of anything from a dozen to thousands of galaxies . Much more mass than in their stars is in diffuse gas, which fills the space between the galaxies. The latter is very hot and consequently could only be discovered when the emergence of space travel paved the way for X-ray astronomy .
The observations made so far suggest that galaxy clusters are gravitationally bound, i. i.e. that they are held together by their own gravity . However, this is not possible if only baryonic matter (stars and gas) is present and the general theory of relativity (GTR) is used.
Possible solutions to this contradiction are
- the introduction of a large amount of not directly visible mass, dark matter. This is not by definition non-baryonic, but there are good arguments for it (see primordial nucleosynthesis and cosmic background radiation , also the second conclusion below).
- or a modification of the ART, e.g. B. Modified Newtonian Dynamics .
Previous observations, e.g. B. the rotation curves of the galaxies or the internal dynamics of galaxy clusters, could only do little to answer this question.
Interpretation of the observations on the bullet cluster
The galaxies fly past one another practically undisturbed (collision-free), as the distance between them and between the stars in them is very large compared to the size of the objects.
On the other hand, the gas clouds in the two piles do not run freely through each other, but shock waves are formed (red in the picture), at the fronts of which the material is heated ; the shock generation is due to the electromagnetic interaction of the gas particles, not to gravitation. Due to the “impact” of the clouds, they lose speed, and so the bullet cluster gas lags behind the galaxies.
Implications for Dark Matter
- It is there. Otherwise the measured gravitational lensing effect cannot be explained. This is important because it sets boundaries for theories that consider modifying the GTR.
- It behaves like the galaxies. That is, it flows almost or completely without bumps through the other pile. The interaction with itself and with the intergalactic gas must therefore be correspondingly weak. This is an indication that dark matter is not baryonic.
- After MOON hypothesis ( Mo difizierte N ewtonsche D ynamik - see above for ART) the center of the deflection of light in the gas to accept would have been, which is not the case, bringing the MOND hypothesis is not confirmed at 1E 0657-558, however, this underpins the dark matter hypothesis.
Similar object
The work on the bullet cluster published in 2006 has since been followed by another publication with the same objective. This deals with the situation in the Abell 520 system, in which similar observations are made as in the bullet cluster. While the considerations made here on the dynamics of the individual components (stars, gas and dark matter) can be transferred directly to the conditions there, the overall situation there is more complex and offers new opportunities to learn something about dark matter.
Individual evidence
- ^ W. Tucker et al .: 1E 0657-56: A Contender for the Hottest Known Cluster of Galaxies' . In: Astrophysical Journal . tape 496 , 1998, pp. L5 , bibcode : 1998ApJ ... 496L ... 5T .
- ↑ Ned Wright's cosmology calculator (English)
- ↑ a b Douglas Clowe et al .: A Direct Empirical Proof of the Existence of Dark Matter . Astrophys. J. 648 , pp. L109-L113, 2006, doi: 10.1086 / 508162 , arxiv : astro-ph / 0608407
- ↑ Jounghun Lee, Eiichiro Komatsu: Bullet Cluster: A Challenge to LCDM Cosmology . In: Astrophysical Journal . 718, June 25, 2010. arxiv : 1003.0939 . bibcode : 2010ApJ ... 718 ... 60L . doi : 10.1088 / 0004-637X / 718/1/60 .
