Researchers discover the largest radio galaxy of all time

A research team led by Martijn Oei, a Dutch doctor. student, identified a radio galaxy – at least 16 million light-years long – by a fluke. The pair of plasma plumes is the largest structure made by a galaxy known to date. The result challenges some long-held assumptions about the evolution of radio galaxies.

Part of LOFAR in Exloo, Drenthe. Image credit: LOFAR.

A supermassive black hole lurking at the center of many galaxies slows the birth of new stars and, in turn, strongly impacts the galaxy’s entire life cycle. Sometimes this can lead to frantic scenarios, where the black hole creates two jet streams, catapulting the building materials of baby stars out of the galaxy at near the speed of light.

In this aggressive process, stardust heats up so much that it dissolves in plasma and glows in the presence of radio light.

The global research team made up of scientists from Leiden (Netherlands), Hertfordshire, Oxford (UK) and Paris (France) have now collected this light with the pan-European LOFAR telescope, the epicenter of which is in a swampy Dutch “radio dark” nature reserve – where a smartphone falls signal deliberately.

Record length

The image of the two plasma plumes is exceptional because scientists have never seen such a huge structure made by a single galaxy. The discovery reveals that the sphere of influence of some galaxies extends far from their direct environment. How far, exactly, is difficult to determine.

As astronomical images are captured from a single vantage point (Earth), they have no depth. As a result, researchers can only quantify a portion of the radio galaxy’s length, which is a poor estimate of the full length. However, even this lower limit, which is more than 16 million light-years away, is enormous and is equivalent to a hundred Milky Ways in a row.

Visible with the Naked Radio Eye

Since the Earth does not have a distinct space in the Universe, it has never been possible for such a huge galactic structure to be in everyone’s backyard. And, in fact, the radio giant is three billion light-years from Earth. Despite this staggering distance, the giant appears as huge as the Moon in the sky – an indication that the structure must have been a record length.

The radio eyes of the LOFAR telescope were able to see the giant due to the fact that the plumes were relatively faint. The researchers were suddenly able to observe the giant, reprocessing a set of images already present in such a way as to bring out subtle patterns.

The Giant Alcyoneus

Scientists have named the giant structure Alcyoneus, after the son of Ouranos, the Greek sky god. For authority over the cosmos, this mythological giant Alcyoneus fought with Heracles and other Olympians. A statue of Alcyoneus is carved in the famous Pergamon Altar, located in Berlin.

ghostly dance

Alcyoneus plumes likely show information about the generally elusive filaments of the cosmic web. The Cosmic Web is an alternative name for the current and evolved universe, which resembles a network of knots and threads that astrophysicists call clusters and filamentsrespectively.

Galaxies are clearly visible in filaments and clusters, but spotting the middle between galaxies only succeeded in clusters, with a few exceptions. Can Alcyoneus change this?

As Alcyoneus hosts a filament, as the Milky Way does, its plumes sense a headwind passing through the middle. This subtly changes the shape and direction of the plumes; they do a slow dance accompanying an invisible partner.

Scientists for many years have proposed that the pressures and shapes of radiogalaxy plumes may be related to the properties of filaments, but they have never found an example where this association is as plausible as with Alcyoneus. Alcyoneus plumes are so huge and exclusive that they can be easily molded by the surrounding environment.

Black holes are cosmic pillars

The cosmic web maintains its shape because the thermal pressure of the medium in the filaments and clusters compensates for the force of attraction of gravity. It has become apparent over the past two decades that glowing stardust, which jet streams blast out of galaxies, is keeping the web warm. In this way, the large-scale structure of our Universe is supported by the central black holes in the galaxy contribution.

Since black holes are very small compared to filaments and clusters, the contribution is even more striking. It’s as if the Earth’s temperature is regulated by something as small as the size of a marble.

Mysterious origin

What remains a mystery, for now, is the answer to “what gave Alcyoneus its record length?” At first, researchers thought that an incredibly huge black hole would have a large stellar population (with lots of stardust) or extremely potential jet streams.

To their surprise, Alcyoneus appears to be below average in all of these aspects compared to his siblings. The scientists intend to examine whether the environments of radio galaxies could explain the evolution of giants.