More than 300 million light-years away from Earth, a jellyfish galaxy flaunts a peculiar pair of bunny ears as it swims (or hops) through the cosmic sea. This galactic jellyfish-bunny hybrid is none other than NGC 4858, a galaxy whose appearance has been molded by the extreme environment surrounding it.
The unique shape of NGC 4858 has now been explained in a recent preprint arXiv paper, which reveals a suite of pressures that sculpt the galaxy’s features. As NGC 4858 wades through a region packed with neighboring galaxies, extreme pressures contort its gaseous material to create the jellyfish and bunny combo.
The Components of a Galaxy Cluster
NGC 4858 is a barred spiral galaxy located within the Coma cluster, a galaxy cluster that is part of the constellation Coma Berenices in the northern sky. Galaxy clusters like the Coma cluster boast hundreds or even thousands of galaxies, although these only make up a small portion of the clusters’ total mass.
The Coma cluster itself contains over 1,000 identified galaxies, most of which are elliptical galaxies that occupy its center. Spiral galaxies like NGC 4858, however, appear at the outskirts of the cluster, defined by swirling arms teeming with young stars. NGC 4858 is thought to have an extremely high rate of star formation, and it is expected to use up all of its gas before it reaches the end of its life.
Accompanying the galaxies is an abundance of hot plasma and dark matter, the latter making up the majority of galaxy clusters. Dark matter is arguably the unsung hero of these clusters, acting as the invisible glue that holds everything together through its gravitational influence.
Galaxy clusters also contain supermassive black holes that play a major role in the birth of the intercluster medium (ICM), a cornerstone of new star formation that consists of hot plasma that fills the space in between galaxies.
Read More: Some 800,000 Galaxies Shine in Our Most Complete Map of the Universe Yet
Building a Jellyfish Galaxy
The new paper found that the shape of NGC 4858 is being warped as it moves through the Coma cluster, experiencing extreme outside pressure called ram pressure or “wind.” The pressure exerted on NGC 4858 has removed much of its interior gas, causing it to narrow and elongate to the point of looking like a jellyfish. It’s even followed by trails of gas and young stars, extending just like jellyfish tendrils.
“This galaxy, NGC 4858, is traveling very quickly through the Coma cluster,” said first author Harrison Souchereau, a doctoral student at Yale University, in a statement. “It is effectively in a wind tunnel, and its gas is in the process of being stripped away by the wind.”
To determine the shape of NGC 4858, researchers examined high-resolution images of molecular gas within the galaxy that were obtained by the Atacama Large Millimeter Array (ALMA) radio telescope. The images came from the ALMA-JELLY program, which is dedicated to surveying similarly shaped galaxies influenced by ram pressure.
Observing Galactic Bunny Ears
The researchers found additional features adorning the jellyfish body of NGC 4858, including bunny ears sprouting from the galaxy. These ears are actually distorted spiral arms that were likely given their shape from a combination of wind pushing on the gas and the rotation of the galaxy itself, according to the researchers.
The researchers also detected “fallback,” in which gas that has been ousted from the galaxy disk falls back toward the disk.
“Most people think of ram pressure stripping as removing the gas from galaxies, which is the main effect and a big deal, since gas is the raw material for star formation,” said Jeffery Kenney, the senior author of the paper in the statement. “But sometimes gas can get pushed out but not stripped, since it never reaches the escape speed. So it falls back, creating a kind of galactic fountain. When this happens, the gas falling back often concentrates in distorted spiral arms on one side of the inner tail.”
Read More: Dueling Galaxies Pierce One Another With a Ray of Radiation in a Cosmic Joust
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Cornell University arXiv. ALMA-JELLY I: High Resolution CO(2-1) Observations of Ongoing Ram Pressure Stripping in NGC 4858 Reveal Asymmetrical Gas Tail Formation and Fallback
Harvard and Smithsonian Center for Astrophysics. Galaxy Clusters
European Space Agency. Knots and bursts
Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
