Scientists are baffled after spotting two galaxies entangled in a 'cosmic joust'

Daily Mail​

21-05-2025

Scientists have been left baffled after spotting two galaxies entangled in a 'cosmic joust'.
Travelling at dizzying speeds of 500 kilometres per second, these two galaxies rush towards each other, only to land a glancing blow and swing around for another attack.
But scientists have spotted that one of the galaxies has an unfair advantage: a deadly 'spear of radiation'.
Using its bright galactic core, known as a quasar, this unsporting galaxy fires a beam of energy powered by a supermassive black hole through its opponent's core.
With each pass, more of the wounded galaxy's gas and dust are fed into the black hole, giving it even more power for the next devastating attack.
Co-lead author Dr Sergei Balashev, of the Ioffe Institute in St Petersburg, Russia, says: 'Here we see for the first time the effect of a quasar's radiation directly on the internal structure of the gas in an otherwise regular galaxy.'
The researchers' new observations suggest that this radiation lance disrupts clouds of gas and dust, leaving behind only the smallest and densest regions.
These surviving regions are too small to produce stars of their own, meaning the wounded galaxy has far fewer stellar nurseries and young stars.
Quasars are some of the brightest objects in the universe, typically producing thousands of times more light than the entire Milky Way.
They are formed when gas and dust fall into a supermassive black hole, spiralling around it before falling in like water around a plug hole.
This gas and dust is subject to extreme gravitational and frictional forces, heating up to millions of degrees and blasting out dazzling jets of material and radiation.
Because quasars require so much matter to get started, some astronomers think they only occur when galaxies merge.
From the intensity of the radiation being emitted, in a paper published today in Nature, the researchers estimate that the black hole powering the quasar is around 100 million times the mass of the sun.
When the beam of radiation emitted by this quasar hits the other galaxy, it has a similar impact to the ignition of a newborn star.
As the blast of UV radiation hits, fields of gas surrounding the galaxy are transformed into clumps with about 10 per cent of the mass of our sun.
Co-lead author Dr Pasquier Noterdaeme, of the Institut d'Astrophysique de Paris, told MailOnline: 'The super intense UV light from the quasar is able to disrupt molecular gas in the other galaxy.
'Only very small dense clumps survive the radiation, but these are too small to sustain star formation.'
Since the quasar radiation pierces the galaxy like a spear, star formation is only inhibited in the 'wounded' region - leaving the rest of the galaxy unaffected.
Over billions of years, Dr Noterdaeme says these two galaxies will eventually 'merge into one'.
Although quasars are extremely bright, there is still a lot scientists don't know about how they interact with other objects.
This is because both quasars and galactic collisions were much more common in the distant past.
That means researchers need to look very far away from Earth to find light that started its journey at an early point in the Universe's history.
Even the closest observable quasars to Earth are about 600 million light years away.
To observe this galactic joust, researchers used two super-powerful telescopes to capture light which has taken 11 billion years to reach Earth.
Combining data from the European Southern Observatory's Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA), the researchers captured images from a time when the Universe was just 18 per cent of its current age.
The two galaxies are so far away from Earth and so close to each other that they seemed to be one object.
It's only thanks to new observations from the ALMA telescope that researchers have been able to tell them apart.
This extremely detailed data has offered scientists an unprecedented look into the effects of an ongoing 'galactic battle'.
In the future, the researchers would like to use even larger, more powerful telescopes to get more data about how these collisions unfold.
Dr Noterdaeme says this would 'certainly allow us to push forward a deeper study of this, and other systems, to better understand the evolution of quasars and their effect on host and nearby galaxies.'
WHAT IS A QUASAR?
'Quasar' is short for quasi-stellar radio source, and describes bright centres of galaxies.
All galaxies have a supermassive black hole at their cores.
When the inflow of gas and dust to this black hole reaches a certain level, the event can cause a 'quasar' to form - an extremely bright region as the material swirls around the black hole.
They are typically 3,260 light-years across.
These regions emit huge amounts of electro-magnetic radiation in their jets, and can be a trillion times brighter than the sun.
But they last only 10 to 100 million years on average, making them relatively tough to spot in galaxies that are several billion years old.
The rapidly-spinning disk spews jets of particles moving outward at speeds approaching that of light.