Largest radio galaxy discovered 3 billion light-years away

The finding disproves some long-kept hypotheses about the growth of radio galaxies.


The international team of scientists from Leiden (The Netherlands), Hertfordshire, Oxford (both UK), and Paris (France)- using the LOFAR telescope- has discovered the largest radio galaxy ever. The galaxy spans at least 16 million light-years and consists of the largest known structure of a pair of plasma plumes.

Scientists named the giant structure Alcyoneus. Lurking some 3 billion light-years away. Alcyoneus’ plumes possibly reveal information about the most elusive filaments of the Cosmic Web.

The pair of plasma plumes are very special. Scientists have never seen such a large structure by a single galaxy. The discovery of this galaxy shows that the sphere of influence of some galaxies reaches far from their direct environment.

It is quite difficult to determine how far. Hence, scientists use pictures captured from a single viewpoint that does not reveal depth. Therefore, scientists can only measure a part of the radio galaxy length.

Even to that lower bound, 16 million light-years is enormous. We can consider it as one hundred Milky Ways in a row.

LOFAR can detect the giant because the plumes are relatively faint. By reprocessing a set of existing images so that subtle patterns stood out, the scientists were suddenly able to spot the giant.

The plumes of this galaxy feel a headwind while moving through the medium, thereby changing the direction and shape of the plumes. As scientists reported, the plumes dance with an invisible partner.

Namely, Alcyoneus’ plumes are so big and rarefied that the surrounding medium can easily mold them.

However, it remains elusive what has given Alcyoneus its record length. Scientists first thought of an exceptionally massive black hole, an extensive stellar population (and so a lot of stardust), or mighty jet streams. But, Alcyoneus appears to be less than average on all these aspects compared to its smaller sisters and brothers.

In the future, scientists are planning to investigate whether the environments of radio galaxies could explain the growth of giants instead.

Journal Reference:

  1. Martijn S.S.L. Oei, Reinout J. van Weeren et al. The discovery of a radio galaxy of at least 5 Mpc. arXiv:2202.05427


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