IC 1101 is a supergiant elliptical galaxy located in the constellation Virgo. With a radius of about 2 million light years and home to 100 trillion stars, it is one of the largest galaxies known, as well as one of the most luminous. The galaxy has an apparent magnitude of 14.73 and lies at an approximate distance of 1.045 billion light years from Earth.
IC 1101 has the classification E/S0 (elliptical to lenticular galaxy) and its exact morphological type is not certain. It is probably an elliptical galaxy, but there has been some debate about the possibility that it may be shaped like a flat disc, which is characteristic of lenticular galaxies. If it is a lenticular galaxy, it is seen at its broadest dimensions when viewed from Earth. However, the sheer size of IC 1101 suggests an elliptical galaxy since most lenticulars are 50,000 to 120,000 light years across.
Image of the giant galaxy IC 1101, taken by the Hubble Space Telescope’s Wide Field and Planetary Camera 2 at 702 nm. Image: NASA/ESA/Hubble Space Telescope
Both elliptical and lenticular galaxies are composed of old stars and contain very little interstellar matter that would feed star formation. However, lenticulars have visible disks and a prominent bulge like spiral galaxies, but they do not have the spiral arm structure. They are believed to be the transitional type between spiral and elliptical galaxies. Ellipticals, on the other hand, do not have a disk or any spiral structure. They have an ellipsoidal shape and appear featureless.
IC 1101, image: NASA – SDSS
Size
The halo of IC 1101 stretches about 2 million light years (600 kiloparsecs) from the core, making the galaxy one of the largest ones discovered to date, with a diameter of about 4 million light years.
IC 1101 has an angular size of 1.20 by 0.60 arcminutes and an effective radius of about 212,000 light years. Also called the half-light radius, the effective radius is the radius at which half of the galaxy’s light is emitted. It does not reflect the galaxy’s actual size, which is difficult to measure because galaxies do not have clear boundaries, but simply get fainter further from the core.
Additionally, a galaxy’s apparent size changes depending on the size and sensitivity of the telescope, as well as on the length of time for which the galaxy is observed. Longer exposures with larger telescopes will always reveal more than shorter ones in smaller instruments. For this reason, the half-light radius is used as a measurement.
The immense size of IC 1101 is believed to be the result of many smaller galaxies merging with each other. The many collisions have stripped the galaxies of star-forming gas and dust, resulting in very little active star formation taking place in IC 1101.
IC 1011 compared to the Milky Way
IC 1101 spans 4 million light years – some estimates even give the galaxy a diameter of 6 million light years – while the Milky Way has a visible diameter of 150,000 to 200,000 light years. The entire Local Group of galaxies, which includes the Milky Way, Andromeda and Triangulum galaxies, spans 9.8 million light years. If IC 1101 replaced our galaxy in the Local Group, it would engulf Andromeda, Triangulum, the Large and Small Magellanic Clouds, and everything in between.
IC 1101 compared to the Milky Way, Andromeda Galaxy and Messier 87, image: Fernando de Gorocica (CC BY-SA 4.0)
Even larger spiral galaxies than Andromeda and the Milky Way fade in comparison to IC 1101. Malin 1 in Coma Berenices and the Condor Galaxy (NGC 6872) in Pavo, both among the largest spiral galaxies known, span 650,000 and 522,000 light years respectively. Messier 87 (Virgo A), the supergiant elliptical galaxy in the centre of the Virgo Cluster, has an estimated diameter of 240,000 light years.
Galaxy size comparison, image: Wikimedia Commons/Sagittarius A (CC BY-SA 4.0)
Stars
IC 1101 contains 100 trillion stars, and they give it a staggering luminosity. In comparison, our galaxy hosts between 100 and 400 billion stars.
However, with very little star-forming activity taking place in IC 1101, the galaxy is left mostly with old, metal-poor stars that will reach the end of their lives in the relatively near astronomical future. The old stars give the galaxy a yellowish hue. They also give it a bleak future. As the stars reach the end of their lives, IC 1101 will gradually shrink and, unless it keeps colliding with younger galaxies, it will eventually fade away.
Black hole
A study published in 2017 reported an exceptionally large core in IC 1101, about 2.77 arcseconds in apparent size. This corresponds to a physical size of 13,700 light years (4.2 kiloparsecs) across, the largest core size in any galaxy observed.
IC 1101 has a bright radio source at the centre, catalogued as PKS 1508+059, which emits two jets and likely corresponds to a supermassive black hole with an estimated mass of 50 to 70 billion solar masses. This is one of the largest black holes ever detected.
Facts
IC 1101 was discovered by the German-born British astronomer William Herschel on June 19, 1790. However, Herschel did not know what he was observing. At the time, galaxies were still believed to be nebulae in the Milky Way. Their true nature was not proven until the 1920s, when Edwin Hubble measured the distance to the Andromeda Galaxy using a Cepheid variable.
IC 1101 is the brightest member of the Abell 2029 cluster of galaxies. The cluster has a diameter of 5.8 to 8 million light years and is one of the densest clusters in the sky. As the brightest member, IC 1101 has the designation A2029-BCG (BCG stands for “brightest cluster galaxy”).
A study published in 1990 reported that the galaxy emitted about 26% of the total light from the cluster, even though it is not the only exceptionally luminous galaxy in the group. Abell 2029 contains thousands of galaxies, including hundreds of giant galaxies.
Abell 2029 is composed of thousands of galaxies (optical image, right) enveloped in a gigantic cloud of hot gas (X-ray image, left), and an amount of dark matter equivalent to more than a hundred trillion Suns. Both the gas and the galaxies are confined to the cluster primarily by the gravity of the dark matter. If this galaxy cluster is a representative sample of the universe, the Chandra observation indicates that 70 to 90 percent of the mass of the universe consists of dark matter – mysterious particles left over from the dense early universe that interact with each other and “normal” matter only through gravity. Image: NASA (Chandra – SDSS II)
The designation IC 1101 comes from the Index Catalogue of Nebulae and Clusters of Stars, first published in 1895 as a supplement to the New General Catalogue (NGC). Most brighter galaxies, nebulae and star clusters are still commonly referred to by their NGC or IC designations. Danish astronomer John Louis Emil Dreyer, who compiled the Index Catalogue, listed the galaxy as the 1101st entry.
Location
IC 1101 is located in the constellation Virgo, near the border with Serpens. It lies in the same area of the sky as the globular cluster Messier 5 and the barred spiral galaxy NGC 5921 (also discovered by William Herschel). However, at magnitude 14.73, the galaxy is considerably fainter than these two objects and requires a larger telescope to be seen. Like all elliptical galaxies, it appears as a ball of light and does not get any more distinctive even in the largest of telescopes.
IC 1101 location, image: Wikisky
IC 1101
| Constellation | Virgo |
| Galaxy type | E/S0 (elliptical to lenticular) |
| Right ascension | 15h 10m 56.100s |
| Declination | +05° 44′ 41.19″ |
| Apparent magnitude | 14.73 |
| Apparent size | 1′.2 × 0′.6 |
| Distance | 1.045 ± 0.073 billion light years (320.4 ± 22.4 megaparsecs) |
| Size (effective radius): | 212,000 ± 39,000 light years (64 ± 12 kiloparsecs) |
| Number of stars | 100 trillion |
| Redshift | 0.0777 |
| Helio radial velocity | 23,368 ± 26 km/s (14,520 ± 16 mi/s) |
| Galactocentric velocity | 23,395 ± 26 km/s (14,537 ± 16 mi/s) |
| Designations | IC 1101, PGC 54167, UGC 9752, A2029-BCG, BWE 1508+0555, GALEX J151056.1+054439, 2MASX J15105610+0544416, NVSS J151055+054439, PKS 1508+05, PKS J1510+0544, PKS 1508+059, SDSS J151056.10+054441.1, RGB J1510+057A, RGB J1510+057B |