Hubble sees a rare ‘bullseye’ galaxy with nine mesmerizing rings

Hubble sees a rare ‘bullseye’ galaxy with nine mesmerizing rings

Collisional ring galaxies (CRGs), such as the Cartwheel galaxy, provide insights into galactic structures and evolution. The collision and expanding rings act as probes, revealing information about the galaxy’s gravitational potential and star formation processes. However, the ring phase lasts only a few hundred million years, and no CRGs with more than three rings have been found. Studying two- or three-ring CRGs remains challenging.

A new study reports the discovery of a “Bullseye” galaxy, a collisional ring galaxy (CRG) with nine rings, the most observed in a CRG.

This discovery was made using NASA’s Hubble Space Telescope. Originally known as LEDA 1313424, a massive galaxy has nine star-filled rings caused by a smaller blue dwarf galaxy that passed through its center. Astronomers using the Hubble Space Telescope identified eight rings, more than ever, and confirmed a ninth ring using data from the W. M. Keck Observatory in Hawaii.

Imad Pasha, the lead researcher and a doctoral student at Yale University in New Haven, Connecticut, said, “This was a serendipitous discovery. In a ground-based imaging survey, I saw a galaxy with several clear rings and had to investigate.”

Hubble and Keck’s observations confirmed that a blue dwarf galaxy passed through the center of the “Bullseye” galaxy about 50 million years ago, creating rings like ripples in a pond. Now, a thin gas trail links the galaxies 130,000 light-years apart.

“We’re seeing the Bullseye at a rare moment,” said Pieter G. van Dokkum, a Yale professor and study co-author.

Galaxy collisions are common, but it’s rare for one to pass through another’s center. The blue dwarf galaxy’s path triggered waves of material movement and new star formation regions.

The Bullseye galaxy is 250,000 light-years across, nearly two-and-a-half times larger than our 100,000 light-year-wide Milky Way.

Researchers used Hubble’s precise vision to identify most of the “Bullseye” galaxy rings, as many are clustered at the center.

“This would have been impossible without Hubble,” said Imad Pasha. They also used Keck to confirm one more ring and suspect a 10th ring existed but has since faded. They estimate it might be three times farther out than the widest ring seen in Hubble’s image.

Pasha discovered that the Bullseye galaxy’s rings had moved outward almost exactly as predicted by models, confirming a long-standing theory.

“If viewed from above, the rings would appear circular, with rings bunched up at the center and spreading out as they move outward,” explained Pasha. Hubble’s image shows the galaxy from a slight angle, making the uneven spacing of the rings more noticeable.

Imagine dropping a pebble into a pond to visualize how the rings formed. The first ring ripples out and becomes the widest, with subsequent rings forming.

Researchers believe the first two rings in the Bullseye formed quickly and spread out in wider circles. Due to the impact of the blue dwarf galaxy, the formation of additional rings may have been slightly staggered.

The orbits of individual stars remained mostly unchanged, but groups of stars “piled up” to form rings over millions of years. Gas was carried outward and mixed with dust, creating new stars and brightening the Bullseye’s rings.

Further research is needed to determine which stars existed before and after the blue dwarf galaxy’s passage. Astronomers can now improve models predicting the galaxy’s evolution over billions of years, including the disappearance of more rings.

This discovery was lucky, but astronomers expect to find more similar galaxies soon. “Once NASA’s Nancy Grace Roman Space Telescope begins operations, interesting objects will pop out much more easily,” explained van Dokkum. We will learn how rare these spectacular events really are.”

Journal Reference:

  1. Imad Pasha, Pieter G. van Dokkum, Qing Liu (刘青), William P. Bowman, Steven R. Janssens, Michael A. Keim, Chloe Neufeld, and Roberto Abraham. The Bullseye: HST, Keck/KCWI, and Dragonfly Characterization of a Giant Nine-ringed Galaxy. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/ad9f5c

Source: Tech Explorist

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