Spectacular Head-On Collision Between Two Galaxies Creates a Tsunami of Starbirth

A spectacular head-on collision between two galaxies fueled the unusual triangular-shaped star-birthing frenzy, as captured in a new image from NASA’s Hubble Space Telescope, Credit: Flatiron Inst. / UWashington, Joseph DePasquale (STScI)

Interactions between these two galaxies are causing a starbirth tsunami.

There's no better site to look at strangely shaped galaxies than the "Arp Catalogue of Peculiar Galaxies."

The catalogue, which was compiled by astronomer Halton Arp in 1966, is a collection of 338 bizarre interacting galaxies. Arp, on the other hand, did not build the list solely to display odd galaxies. These strange galaxies, he reasoned, would be good laboratories for studying the physical processes that deform normal-looking elliptical and spiral galaxies. He was one of the first to propose that galactic collisions could result in the formation of stars in bursts.

His viewpoint differed from that of many astronomers in the 1960s, who dismissed malformed galaxies as simple anomalies. They thought the universe was "cookie-cutter," with most galaxies being tidy and symmetrical. Arp, on the other hand, believed in a universe full of conflict and birth.

This Hubble Space Telescope image of the Arp 143 system shows one such Arp galaxy that is erupting with new stars. This system's two galaxies collided head-on, igniting a triangular-shaped surge of star creation. The twisted, star-forming spiral galaxy NGC 2445 is on the right, and its less showy neighbour, NGC 2444, is on the left.

The peculiar triangular-shaped star-birthing frenzy was powered by a spectacular head-on collision between two galaxies, as caught in a new image from NASA's Hubble Space Telescope.

Arp 143 is the name given to the interacting galaxy couple. The duo includes the star-forming spiral galaxy NGC 2445 on the right, and its less showy partner, NGC 2444 on the left.

The galaxies may have gone through each other, triggering the star-formation inferno in NGC 2445, where thousands of stars are bursting to life on the right-hand side of the image, according to astronomers. Because it is rich in gas, the fuel that creates stars, this galaxy is flooded in starbirth. It hasn't yet escaped the gravitational grasp of its partner NGC 2444, which can be seen on the image's left side. NGC 2444 looks to be winning a cosmic tug-of-war between the two stars. NGC 2445 has been drained of gas, resulting in the bizarre triangle of newly formed stars.

"Simulations demonstrate that colliding galaxies create rings of new stars," said astronomer Julianne Dalcanton of the Flatiron Institute's Center for Computational Astrophysics in New York and the University of Washington in Seattle. "As a result, star formation rings are prevalent. What's strange about this system, however, is that it's a triangle of star formation. Part of the reason for this form is that two galaxies are still so close together, and NGC 2444 is still gravitationally bound to the other galaxy. NGC 2444 may possibly contain a hot ring of gas that helps to drive the gas from NGC 2445 away from its centre. So they aren't fully free of one other yet, and their strange relationship is warping the ring into this triangle."

NGC 2444 also pulls taffy-like strands of gas from its companion, fuelling the streamers of young, blue stars that appear to form a bridge between the two galaxies.

These streamers are part of what appears to be a wave of star formation that began on the periphery of NGC 2445 and moved inside. The streamer stars are thought to have been born between 50 and 100 million years ago, according to researchers. However, as NGC 2445 continues to drift away from NGC 2444, these young stars are being left behind.

Closer to the core of NGC 2445, stars no older than 1 million to 2 million years are developing. The clarity of Hubble's vision exposes several individual stars. They are the galaxy's brightest and most massive stars. The majority of the vivid blue clumps are star clusters. The pink blobs are massive, newly formed star clusters that are still covered in dust and gas.

Although the majority of the action takes place in NGC 2445, this does not mean that the opposite side of the interacting pair is unaffected. The gravitational tug of war has bent NGC 2444 into an unusual shape. Because it lost its gas long ago, well before this cosmic encounter, the galaxy contains old stars and no new starbirth.

"This is a recent illustration of the types of exchanges that occurred in the past." Elena Sabbi of the Space Telescope Science Institute in Baltimore, Maryland, stated, "It's a terrific playground for understanding star formation and interacting galaxies."

NASA and the European Space Agency collaborated on the Hubble Space Telescope (European Space Agency). The telescope is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Hubble science operations are managed by the Space Telescope Science Institute (STScI) in Baltimore, Maryland. The Association of Universities for Research in Astronomy in Washington, D.C. manages STScI for NASA.

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