An international team of astronomers has discovered a “cosmic ring of fire”, a gigantic donut-shaped galaxy some 11 billion light-years distant from Earth. This type of galaxy is extremely rare, especially for its age, and was likely caused by a collision with a smaller galaxy that can still be seen near the scene of the “cosmic accident.”
The galaxy, called R5519 and roughly the mass of the Milky Way , is circular, with a hole in the middle. A ring galaxy. Their discovery, announced in the journal Nature Astronomy , will shake up theories about the earliest formation of galactic structures and how they evolve.
A unique object in the early universe
“It is a very curious object that we have never seen before,” Tiantian Yuan of the ARC Australia Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3-D). “It seems strange and familiar at the same time.” Not surprisingly, it is the first collision ring galaxy to be found in the early universe.
The black hole at the center of this galaxy is incredibly massive, with a diameter 2 billion times longer than the distance between the Earth and the Sun. To put it another way, it is three million times larger than the diameter of the black hole. supermassive in the Messier 87 galaxy, which in 2019 became the first to be directly photographed.
The outer edge of the R5519 ring is quite large, about 42,400 light-years in diameter (on average). The center, with no detectable trace of the star-filled bulge that normally fills a galactic center. And it is huge. For comparison, if our local galaxy had such a large hole at its center, it would extend beyond the solar system.
However, the ring exhibits a spectacular star formation rate: about 80 new solar-mass stars are born each year. About 50 times more than the Milky Way. This suggests a gravitational disruption perhaps due to another galaxy passing through R5519, sending out density waves that propagate radially outward.
As these waves push and condense gas and dust in the galaxy, it triggers star formation by facilitating the gravitational collapse of clumps of dust that turn into intensely blue baby stars.
How is it shaped like a ring?
The researchers claim that this unusual shape was likely caused by a violent encounter with another galaxy . In its day, R5519 would have had a thin disk silhouette, until a smaller galaxy hit the center of it. The gravitational effects of the collision would have sent the stars rippling outward, leaving the center almost empty. This is a particularly rare event : collision ring galaxies are about 1,000 times rarer than usual. And this is one of a kind.
“The thin disk is the defining component of spiral galaxies: before they were assembled, the galaxies were in a disordered state, not yet recognizable as spiral galaxies,” adds Kenneth Freeman, co-author of the work.
“In the case of this ring galaxy, we are looking back at the early universe 11 billion years, at a time when the thin discs were just assembling. By comparison, the thin disc of our Milky Way began to coalesce. only 1 billion years ago. This discovery is an indication that the disk assembly in spiral galaxies occurred over a longer period than previously thought. “
It seems we still have a lot to discover about the early years of the universe.
Referencia: A giant galaxy in the young Universe with a massive ring, Nature Astronomy (2020). DOI: 10.1038/s41550-020-1102-7 , www.nature.com/articles/s41550-020-1102-7
