In a groundbreaking revelation, astronomers have utilized NASA’s Chandra X-ray Observatory to unveil the extraordinary phenomenon of “cosmic collisions” within the immense realm of the universe. The observation reveals that NGC 4839, a conglomerate of galaxies, is presently engaged in a collision course with the awe-inspiring Coma galaxy cluster, resulting in the creation of an enormous tail composed of intensely heated plasma.

This momentous discovery provides valuable insights into the growth of galaxy clusters, which are among the largest entities in existence. These new findings, focusing on cosmic collisions, were recently presented at the American Astronomical Society’s 242nd meeting, deepening our understanding of the tremendous width and extent of these cosmic formations. When galaxies come together through the force of gravity, they give rise to smaller gatherings called “galaxy groups” or larger collections called “galaxy clusters.”

Galaxy groups are typically made up of 50 galaxies, whereas clusters might contain hundreds or even thousands of individual galaxies. These cosmic entities are predominantly composed of hot, diffuse gas observed most effectively through X-ray imaging. Despite their thin and sparse nature, these superheated gas reservoirs play a pivotal role in understanding the dynamics of galaxy clusters and groups.

NGC 4839 and the Coma Cluster:

NGC 4839, located on the periphery of the massive Coma galaxy cluster, lies approximately 340 million light-years away. As NGC 4839 advances towards the core of the Coma cluster, its hot gas interacts with the surrounding gas, giving rise to the formation of a prominent tail. This tail, stretching behind NGC 4839, serves as a visible manifestation of the intricate processes occurring within this cosmic collision.

Cosmic Collisions
Image credit: X-ray: Chandra: NASA/SAO/Univ. of Alabama/M. S. Mirakhor et al.; XMM: ESA/XMM-Newton; Optical: SDSS; Image processing: N. Wolk

Astronomers skillfully obtained a remarkable X-ray perspective of the Coma galaxy cluster by utilizing ESA’s XMM-Newton satellite, along with optical information sourced from the Sloan Digital Sky Survey. Within this composite image, NGC 4839 can be seen in the lower right corner. A closer examination using the Chandra X-ray Observatory revealed the brightest galaxy in the group and the densest gas concentrated near the head of NGC 4839’s tail, which extends towards the right. This tail, measuring a staggering 1.5 million light-years in length, represents the broadest ever recorded behind a group of galaxies.

Significance of the Tail:

The brightness of the tail provides astronomers with a unique opportunity to investigate the properties of the gas before it merges with the vast reservoir of hot gas in the Coma Cluster, eventually becoming too faint to observe. By studying the gas within NGC 4839’s tail, scientists can gain valuable insights into the physical processes and dynamics at play within these cosmic collisions.

NGC 4839 and Coma cluster
Image credit: X-ray: Chandra: NASA/SAO/Univ. of Alabama/M. S. Mirakhor et al.; XMM: ESA/XMM-Newton; Optical: SDSS; Image processing: N. Wolk

Shock Wave and Turbulence:

Through Chandra data analysis, researchers identified a shock wave, akin to the sonic boom of a supersonic jet, indicating that NGC 4839 is hurtling through the Coma cluster at a staggering speed of approximately 3 million miles per hour. Additionally, scientists investigated the turbulence within the tail’s gas and found it to be relatively minor, suggesting modest heat conduction within NGC 4839.

Kelvin-Helmholtz Instabilities:

Researchers also detected the presence of Kelvin-Helmholtz instabilities on one side of the tail. These unusual structures, commonly observed in various celestial and terrestrial phenomena, arise from differences in the speed of flowing layers of gas or fluid. The occurrence of Kelvin-Helmholtz instabilities in NGC 4839 suggests either a weak magnetic field or a viscous nature of the gas within the tail.

Implications of the Discovery:

Previous observations estimated the length of NGC 4839’s tail to be at least one million light-years. However, the latest Chandra data has revealed an astonishing new record-breaking length of 1.5 million light-years. This significant increase in the estimated size of the tail highlights the dynamic nature of galactic interactions and the need for continuous exploration and observation to deepen our understanding of these cosmic phenomena.


The collision between NGC 4839 and the Coma galaxy cluster has unveiled a truly awe-inspiring spectacle in the vastness of space. The discovery of the massive tail extending over 1.5 million light-years behind NGC 4839 has provided astronomers with a unique opportunity to study the gas dynamics and physical processes associated with galactic collisions. The extensive research conducted by NASA’s Chandra X-ray Observatory has yielded invaluable understanding regarding the formation and evolution of galaxy clusters, shining a beacon of illumination on the fundamental forces that sculpt the colossal structures within our vast universe. The scientific community eagerly awaits future insights that will enhance our understanding of the cosmos we inhabit as we continue to unravel the secrets of these cosmic encounters.

Astronomers have discovered a giant black hole at the center of Messier 84 “M84” (a massive elliptical galaxy). This giant black hole is leaving an “H”-shaped structure in the multimillion-degree gas around it. Using NASA’s Chandra X-ray Observatory, researchers mapped the hot gas in and around M84. This reveals the letter “H” formed by cavities in the hot gas around the black hole created by jets of particles blasted away from the black hole. The study also shows that the jets may affect the flow of hot gas toward the black hole, slowing the rate at which gas falls onto it. The results were reported in the Royal Astronomical Society Monthly Notices.

With what appears to be a single letter etched into the X-ray glow surrounding it, a massive black hole at the center of an elliptical galaxy is leaving its imprint on its surroundings.

The H-shaped Structure in M84’s Gas Cavity:

A comprehensive new X-ray map of the multimillion-degree gas surrounding the galaxy Messier 84 (M84) reveals this “H”-shaped structure. As gas is captured by the black hole’s gravitational force, a portion of it will descend into the abyss, never to be seen again. Some of the gas, however, escapes this fate by being expelled from the black hole in the form of particle streams. These projectiles can eject holes from the hot gas surrounding the black hole. 

Given the orientation of the jets toward Earth and the profile of the heated gas, it appears that the cavities in Messier 84 resemble the letter “H.” The H-shaped structure in the gas is an illustration of pareidolia, which occurs when individuals perceive familiar shapes or patterns in random data. Pareidolia can occur in all types of data, including images of clouds, mountains, and astronomical objects.

messier 84
Credits: X-ray: NASA/CXC/Princeton Univ/C. Bambic et al.; Optical: SDSS; Radio: NSF/NRAO/VLA/ESO; Image processing: NASA/CXC/SAO/N.Wolk

What is the significance of the NASA Chandra X-ray Observatory?

Using NASA’s Chandra X-ray Observatory, astronomers created a map of the hot plasma (pink) in and around Messier 84, reaching within 100 light-years of the central black hole of the galaxy. This gas radiates at temperatures in the tens of millions of degrees, allowing X-rays to be its primary mode of observation. The enormous letter “H” is approximately 40,000 light-years tall, or roughly half of the Milky Way’s girth. 

The radio image from the Karl G. Jansky Very Large Array (VLA) of the National Science Foundation (blue) reveals the plumes emanating from the black hole. Sloan Digital Sky Survey optical data (white) depicts M84 and neighboring galaxies. The letter H and the black hole’s location are labeled. A further image depicts a zoomed-in view of the region marked with a square, as well as distinct labels for the galaxy and jets in the optical and radio images, respectively.

Do jets have a greater influence on the flow of matter towards a black hole than the black hole’s gravitational pull in Messier 84?

Jets may influence the flow of hot gas toward the black hole even more than the black hole’s gravitational pull, according to researchers investigating M84 with Chandra and the VLA. For instance, the team estimates that matter falls towards the black hole from the north — along the direction of the jet seen in radio waves — at a rate of approximately 500 times the mass of the Earth per year, compared to a rate that is only a quarter of that from directions where the jet is not pointing, such as the east and west. The cavities may lift gas in the direction of the jet, slowing the rate at which gas descends onto the black hole.

The Bondi accretion mode:

The authors tested the Bondi accretion model, in which all matter within a certain distance from a black hole — effectively within a sphere — is near enough to be affected by a black hole’s gravity and begin falling inwards at the same rate from all directions. (The dashed circle in the close-up image is centered on the black hole and indicates the approximate distance at which gas should begin to descend inwards.) 

This effect is named after the astronomer Hermann Bondi, and “accretion” refers to matter plummeting into a black hole. The new results indicate that Bondi accretion is not occurring in Messier 84 because the matter is not descending uniformly from all directions into the black hole.

How does the black hole in Messier 84 compare to the one in M87?

Both Messier 84 and Messier 87 are located in the Virgo Cluster and contain supermassive black holes. The black hole in M87 was the first one captured by the Event Horizon Telescope network, while the black hole in M84 is one of the few black holes close enough to Earth for astronomers to study in detail. 

While both black holes produce a discharge of particles, the point source of X-rays from material closer to the black hole is over ten times fainter in M84 than in M87. This allows astronomers to analyze gas falling towards the black hole in Messier 84 that is further away, as the faint X-rays produced by this gas are not overwhelmed by the X-ray glare from the point source.

The publication of the analysis:

The Monthly Notices of the Royal Astronomical Society will publish a paper describing these results, and a preprint is available here. Christopher Bambic, a graduate student at Princeton University, directed the research along with other authors.