Bullet Cluster

1E 0657-558 (also known as the Bullet Cluster, German " basement pile ") is a cluster of galaxies in the constellation keel of the ship. The exact coordinates of the cluster are right ascension and declination 6582906h 58m 29s Expression error: Missing operand for - 55 ° 57 '. The redshift is z = 0.296, which corresponds to a distance ( time of flight ) of 3.35 billion light years.

Description and significance

Observations in X-rays showed that the bullet cluster actually consists of two clusters of galaxies. By far the more massive of the two is located in the east ( left) and about 100 million years before the observed time was crossed by the second, smaller. This like a bullet, hence the name appears (in the west or right) in the X-ray images. Both clusters have a significantly increased density of galaxies and are now observed at a distance of about 0.72 Mpc. The radial velocities differ only slightly, so that the collision must have occurred approximately in the plane of the sky.

Independently three core sizes were investigated in detail in the Bullet Cluster:

• The distribution of galaxies (observations in visible light )
• The distribution of the intergalactic plasma ( red in the image; observations in X-rays with the Chandra telescope) and
• The distribution of mass and the gravitational potential ( blue in the picture; observations of the gravitational lens effect to images from the Hubble Space Telescope ); this effect is quite small and is reflected in a distortion of the images of background galaxies down ( here a statistical approach must then be made ).

It was found that the individual components of the cluster are unusually clearly separated: the distribution of mass ( dark matter ) follows the distribution of galaxies; the intergalactic gas ( " bright " baryonic matter ) does not, it " lags " behind the Bullet cluster.

This observation constitutes direct empirical evidence for the existence of dark matter and makes 1E 0657-558 an extraordinarily important subject for research.

Explanation

Binding mechanism of galaxy clusters?

Galaxy clusters are accumulations of a dozen to thousands of galaxies. Much more mass than their stars is located in diffuse gas that fills the space between the galaxies. The latter is very hot and could therefore only be discovered when the emerging space of X-ray astronomy paved the way.

The previous observations suggest that clusters of galaxies are gravitationally bound, which means that they are held together by their own gravity. However, this is not possible if only the baryonic matter (stars and gas) is present and the General Relativity (GR ) is assumed.

Possible solutions to this contradiction are

• The introduction of a large quantity is not directly visible mass of dark matter. This is not nichtbaryonisch by definition, but there are good arguments for it ( see primordial nucleosynthesis and cosmic microwave background radiation, also below the second conclusion ).
• Or a modification of ART, such as the Modified Newtonian dynamics.

Previous observations, such as the rotation curves of galaxies and the (internal ) dynamics of galaxy clusters, could do little to answer this question.

Interpretation of the observations at the Bullet Cluster

The galaxies fly virtually undisturbed ( without collision ) past each other, since both the distance between them and between the stars in each of them is very large compared to the extent of the objects.

In contrast, the gas clouds of the two clusters passed through each other not bumpless, but form shock waves (red in the picture ), at the front it comes to heating of the material; shock formation is due to the electromagnetic interaction of the gas and not on the gravity. Through the " impact " of the clouds they lose in speed, and so the Bullet cluster gas lags behind the galaxies.

Implications for dark matter

The same object

Published in 2006, working for Bullet Cluster is now followed another publication with the same objective. This deals with the situation in Abell 520 system, are made in the similar observations as in the Bullet Cluster. While the observations made ​​here on the dynamics of the individual components (stars, gas and dark matter ) can be directly transferred to the local conditions, the overall situation there is complex and offers new opportunities to learn something about the dark matter.