The text and images in this article were originally published on February 8, 2016, and reflect information about NGC 4889 available at that time.
The Sleeping Giant—Elliptical Galaxy NGC 4889
The majestic yet placid appearance of this serene galaxy, NGC 4889, is deceiving to the unsuspecting observer. Captured in this NASA/ESA Hubble Space Telescope image, it harbors a dark secret. At the heart of this giant elliptical galaxy lurks one of the most massive black holes ever discovered.
Located about 300 million light-years away in the Coma Cluster, NGC 4889—the brightest and largest galaxy in this image—is home to a record-breaking supermassive black hole. Twenty-one billion times the mass of the Sun, this black hole has an event horizon—the surface at which even light cannot escape its gravitational grasp—with a diameter of approximately 80 billion miles. This is about 15 times the diameter of Neptune’s orbit around the Sun. By comparison, the supermassive black hole at the center of our galaxy, the Milky Way, is believed to have a mass about four million times that of the Sun and an event horizon just one fifth the orbit of Mercury.
In its deep, dark past, NGC 4889’s black hole was swallowing stars and devouring dust. Astronomers believe that the gigantic black hole has stopped feeding, and is currently resting after feasting on NGC 4889’s cosmic cuisine. The environment within the galaxy is now so peaceful that stars are forming from its remaining gas and orbiting undisturbed around the black hole.
When it was active, the supermassive black hole residing at the nucleus of NGC 4889 was fuelled by the process of hot accretion. When galactic material—such as gas, dust and other debris—slowly fell inwards towards the black hole, it accumulated and formed an accretion disk. Orbiting the black hole, this spinning disk of material was accelerated by the black hole’s immense gravitational pull and heated to millions of degrees. This heated material also expelled gigantic and very energetic jets. During its active period, astronomers would have classified NGC 4889 as a quasar and the disk around the supermassive black hole would have emitted up to a thousand times the energy output of the Milky Way.
The accretion disk sustained the supermassive black hole’s appetite until the nearby supply of galactic material was exhausted. Now, napping quietly as it waits for its next celestial snack, the supermassive black hole is dormant. However its existence allows astronomers to further their knowledge of how and where quasars, these still mysterious and elusive objects, formed in the early days of the Universe.
Featured Image Credit: NASA and ESA
Acknowledgment: J. Clakeslee (Dominion Astrophysical Observatory) and J. Schmidt
Fast Facts about NGC 4889
About this Object
| Object Name: | NGC 4889 |
| Description: | Giant Elliptical Galaxy in the Coma Cluster |
| Position (J2000.0): | RA: 13h 00m 08.13s Dec: +27° 58′ 37.20” |
| Constellation: | Coma Berenices |
| Distance: | 300 million light-years (92 million parsecs) |
About this Data
| Data Description: | The HST data were taken from proposals 11711: J. Blakeslee, P. Cote, and L. Ferrarese (Dominion Astrophysical Observatory), J. Jensen (Utah Valley University), A. Jordan (Pontificia Universidad Catolica de Chile), S. Mei (Observatoire de Paris), E. Peng (Peking University), and J. Tonry (University of Hawaii). |
| Instrument: | ACS/WFC |
| Filters: | F475W (SDSS g) and F814W (I) |
| Exposure Dates: | March 1–2, 2013 |
About this Image
| Credit: | NASA and ESA |
| Release Date: | February 8, 2016 |
| Color: | This image is a composite of separate exposures acquired by the ACS/WFC instrument. Several filters were used to sample various wavelengths. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: F475W (g) – blue F475W (g) +F814W (I) – green F814W (I) – red |
Additional Images of NGC 4889
F475W (g) 
F814W (I) 
Orientation/Scale
NGC 4889 (Hubble Processing) by Amateur Hubble Image Processor Judy Schmidt
A dominant member of the Coma Cluster, remarkable elliptical shell galaxy NGC 4889 looms large over its domain. Within the cluster, only NGC 4874 (not shown) is brighter, and only just barely.
The faintly visible shells of the galaxy are evidence that the monstrous galaxy recently merged with a smaller galaxy.
Other details to notice include smaller and/or more distant elliptical galaxies, some of which are ghostly and faint. I have seen them called them fluffy galaxies in this recent press release. The nature of these ultra-diffuse galaxies and specifically how they manage to form as they do is still a matter of speculation.
Very few Milky Way stars are visible within the field. As usual, the ones with four spikes are most likely foreground stars. The hundreds of tiny, fainter point-like objects are globular clusters, many of which are likely orbiting NGC 4889.
Do you think that maybe some background galaxies show a curious alignment? You might not be imagining it. It’s possible that some weak gravitational lensing is going on. Weak gravitational lensing is detectable by taking measurements of all the background galaxies and seeing if they all seem a bit squished in a certain direction.
One final curiosity that I would like to note about NGC 4889: If you measure the brightness of the center of its nucleus, it is actually not as bright as NGC 4886, which is the smaller elliptical galaxy just above it in this image (that one skinny galaxy is kind of pointing toward it). The way some elliptical galaxies have diffuse cores while others have very sharp ones is something that perplexes me. It seems that even though NGC 4889 is much larger than NGC 4886, its nucleus is notably less dense than NGC 4886’s.
Red: ACS/WFC F814W (jb2i02020_drc)
Green: Pseudo
Blue: ACS/WFC F475W (jb2i02010_drc and jb2i03010_drc)
North is NOT up. It is 43.6° counter-clockwise from up.
Image Processing Credit: Judy Schmidt
Data: from Hubble Archive
