Monster galaxy turns cannibal

Supermassive galaxy (ESO 146-IG 005) is clearly visible in the centre of a galaxy group

A supermassive galaxy (ESO 146-IG 005) is clearly visible in the centre of a galaxy group, along with the remains of at least four other galaxies that are being “digested” by it. ESO 146-IG 005 is thought to be the most massive galaxy in our local universe.

  • 30 trillion times the Sun’s mass
  • Biggest galaxy in our neighbourhood
  • Cosmic cannibal, eating other galaxies

A newly discovered “gravitational lens” in a relatively nearby galaxy cluster is leading astronomers to conclude that the cluster hosts the most massive galaxy known in our local universe.

The study also reaffirms that galactic cannibalism is one reason that this galaxy is so obese, tipping the scales at up to 30 trillion times the mass of our Sun.

The supermassive galaxy is located at the core of the galaxy cluster Abell 3827, which lies some 1.4 billion light-years away. This galaxy and hundreds of its smaller cluster companions are visible in a dramatic new image released by the Gemini Observatory.

The image is part of an upcoming scientific paper that reports on the study of the massive galaxy using the gravitational lens formed by its core (also visible in the image) to provide new measurements of the galaxy’s extreme mass.

Although this bright galaxy (known as ESO 146-IG 005) dominates the core of Abell 3827, “the magnitude of its appetite has not been fully appreciated,” said Gemini astronomer Rodrigo Carrasco, who is a member of the team that used the 8-metre Gemini South telescope in Chile to study this galaxy and its cluster. The Gemini observations revealed, for the first time, the effects of gravitational lensing near the core of ESO 146-IG 005.

Distant galaxies distorted by the gravity of a foreground galaxy

The giant galaxy's gravity acts like a lens to distort the shape of galaxies that lie way beyond, making them look like streaks and arcs.

A gravitational lens is created when a massive object (in this case the core of the supermassive galaxy) distorts its local space. Light from a more distant background galaxy (in this case two galaxies) that is passing by appears deflected from its original path.

From our perspective, we see the background galaxies’ light reshaped as a ring-like structure and arcs around the lensing object. These arcs from both galaxies are clearly visible in the new Gemini images.

“The gravitational lens we discovered allowed us to estimate for the first time the mass of this monster galaxy very accurately. The inferred mass is a factor of 10 greater than previous estimates derived from X-ray observations,” said Carrasco. “Assuming our model is correct, this is by far the most massive galaxy known in our local universe.”

This galaxy’s a messy eater

The exceptional galaxy was not simply born massive; it has grown by consuming its companions in perhaps the most extreme example of ongoing “galaxy cannibalism” known.

“This unabashed cannibal is something of a messy eater, with the partially digested remains of at least four smaller galaxies still visible near its centre,” said team member Michael West, astronomer at the European Southern Observatory.

“Eventually this galaxy will grow even bigger judging by the number of nearby galaxies already within its gravitational grasp.”

These observations yield important insight into the process of galaxy growth, especially of elliptical-shaped galaxies; these galaxies do not appear to have acquired their full mass quickly in the early universe, but instead show significant growth through mergers and cannibalism at later times, after many of their stars have formed. The resulting galaxies, such as this one, can be extremely massive.

The Gemini observations were made using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope in Chile. Follow-up spectroscopic observations used the same instrument to confirm the distances of the two background galaxies whose light is diverted by the gravitational potential of the cluster core. These two galaxies were found to lie at about 2.7 and 5.1 billion light-years away.

The enclosure of the Gemini South observatory in Chile.

The Gemini South observatory in Chile.

The international Gemini Observatory

The Gemini Observatory is an international collaboration with two identical 8-metre telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawai’i (Gemini North), and the other telescope at Cerro Pachon in northern Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources.

The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Science and Technology Facilities Council (STFC), the Canadian National Research Council (NRC), the Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq).

Adapted from information issued by Gemini Observatory / Gemini Legacy Image: R. Carrasco et al., Gemini Observatory/AURA.

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