Galaxies observed as they existed 11.4 billion years ago

22/5/2025 6:19

Astronomers have observed

two distant galaxies - both possessing roughly as many stars as

our Milky Way - careening toward each other before their

inevitable merger at a time when the universe was about a fifth

its current age, a scene resembling two knights charging in a

joust.



The galaxies, observed using two Chile-based telescopes,

were seen as they existed about 11.4 billion years ago,

approximately 2.4 billion years after the Big Bang event that

initiated the universe.



At the heart of one of the galaxies resides a quasar, a

highly luminous object powered by gas and other material falling

into a supermassive black hole. The intense radiation across the

electromagnetic spectrum unleashed by the quasar is seen

disrupting clouds of gas and dust, known as molecular clouds, in

the other galaxy.



It is molecular clouds that give rise to stars. But the

effects of the quasar's radiation turned the clouds in the

affected region into "only tiny dense cloudlets that are too

small to form stars," said astrophysicist Sergei Balashev of the

Ioffe Institute in Saint Petersburg, Russia, co-lead author of

the study published on Wednesday in the journal Nature.



This is the first time such a phenomenon has been observed,

Balashev said.



Stars form by the slow contraction under gravity of these

clouds, with small centers taking shape that heat up and become

new stars. But the galaxy affected by the quasar's radiation was

left with fewer regions that could serve as such stellar

nurseries, undermining its star formation rate.



The interaction between the two galaxies reminded the

researchers of a medieval joust.



"Much like jousting knights charging toward one another,

these galaxies are rapidly approaching. One of them - the quasar

host - emits a powerful beam of radiation that pierces the

companion galaxy, like a lance. This radiation 'wounds' its

'opponent' as it disrupts the gas," said astronomer and co-lead

author Pasquier Noterdaeme of the Paris Institute of

Astrophysics in France.



Supermassive black holes are found at the heart of many

galaxies, including the Milky Way. The researchers estimated the

mass of the one that serves as the engine of the quasar studied

in this research at about 200 million times that of our sun.



The intense gravitational strength of the supermassive black

hole pulls gas and other material toward it. As this stuff

spirals inward at high speed, it heats up due to friction,

forming a disk that emits extremely powerful radiation in two

opposite directions, called biconical beams.



The ultraviolet light from one of these beams is what played

havoc with the gas in the companion galaxy.



This supermassive black hole is much more massive than the

one at the center of the Milky Way - called Sagittarius A*, or

Sgr A* - which possesses roughly 4 million times the mass of the

sun and is located about 26,000 light-years from Earth. A

light-year is the distance light travels in a year, 5.9 trillion

miles (9.5 trillion km).



The researchers used the Atacama Large

Millimeter/submillimeter Array, or ALMA, to characterize the two

galaxies and used the European Southern Observatory's Very Large

Telescope, or VLT, to probe the quasar as well as the gas in the

companion galaxy.



The configuration of the galaxies as viewed from the

perspective of Earth enabled the researchers to observe the

radiation from the quasar passing directly through the companion

galaxy.



Most galactic mergers that have been observed by astronomers

occurred later in the history of the universe.



"Galaxies are typically found in groups, and gravitational

interactions naturally lead to mergers over cosmic time,"

Noterdaeme said. "In line with current understanding, these two

galaxies will eventually coalesce into a single larger galaxy.

The quasar will fade as it exhausts the available fuel."