Hubble Space Telescope Captures Galaxies Caught in Triangular Tug-of-War

A collision between two galaxies may have sparked the odd shape

An image taken by the Hubble Space Telescope of two galaxies interacting with eachother. The galaxy on the right is surrounded by sparkling blue young stars. The galaxy towards the left is smaller and is not as flashy.
Head-on collisions between galaxies like the one seen in Arp 143 (pictured) may be how rings of new stars form.
  NASA, ESA, STScI, Julianne Dalcanton Center for Computational Astrophysics, Flatiron Inst. / UWashington)

The Hubble Space Telescope captured the aftermath of a head-on collision between two galaxies that formed a glittering triangle of cosmic dust and newborn stars, per a NASA statement.

The image feature a galactic pair dubbed Arp 143, with spiral galaxy NGC 2445 on the right and NGC 2444 on the left. The galaxies appear to have collided with each other at some point, creating the dazzling, star-forming swirls seen on the right. Astronomers also suspect that the bright galaxy NGC 2444 has a greater gravitational force and is pulling on NGC 2445, creating the glittering triangle of cosmic dust and newborn stars, per a statement. Studying galactic collisions like Arp 143 may allow astronomers to further understand ring star formation and evolution. 

"Part of the reason for that shape is that these galaxies are still so close to each other, and NGC 2444 is still holding on to the other galaxy gravitationally. NGC 2444 may also have an invisible hot halo of gas that could help to pull NGC 2445's gas away from its nucleus. So, they're not completely free of each other yet, and their unusual interaction is distorting the ring into this triangle," Julianne Dalcanton, an astronomer at the Flatiron Institute's Center for Computational Astrophysics in New York and the University of Washington in Seattle, said in a statement.

Head-on collisions between galaxies trigger star formation after clouds of gas slam into each other. The violent crash triggers shockwaves that spark the collapse of dark nebulae to form stars. Previously, simulations have shown collisions may be crucial for ring formation in new stars. For example, the Cartwheel Galaxy formed after two galaxies smashed together and sports star-flecked rings. When a small galaxy whipped through the middle of an even bigger galaxy, it created ripples that swept up gas in dust, similar to waves made by a stone hitting water.

NGC 2445 appears flashy because it is rich in gassy fuel and holds thousands of infant stars. In the image, young blue stars are seen streaming towards NGC 2444 because its immense gravity is pulling strands of gas from NGC 2445. These stars were created between 50 million and 100 million years ago, but they remain stuck as the two galaxies continue to pull at each other, reports's Elizabeth Howell. It is suspected that these stars were the first to appear during a star-forming frenzy that began outside NGC 2445 and then made its way inward, per a statement.

While NGC 2444 is tugging on NGC 2445, the stars leave a blue-hued bridge between the galaxies as NGC 2445 also pulls away slowly. The bright pink specks are young star clusters still shrouded in dust and gas, a statement explains.

Astronomers suspect NGC 2444 does not appear as stunning because it is filled with much older stars, and its shimmering cosmic gas and dust were long gone before the collision occurred, per A statement explains that no new star formation has been seen in this galaxy.

"This is a nearby example of the kinds of interactions that happened long ago. It's a fantastic sandbox to understand star formation and interacting galaxies," said Elena Sabbi, an astronomer at the Space Telescope Science Institute in Baltimore, in a statement.