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Face to face with a galactic giant

NGC 4911

A Hubble Space Telescope image of spiral galaxy NGC 4911. Thousands of other galaxies of varying sizes and brightnesses also can be seen.

A long-exposure Hubble Space Telescope image shows a majestic face-on spiral galaxy located deep within the Coma Cluster of galaxies, which lies 320 million light-years away in the northern constellation Coma Berenices.

The galaxy, known as NGC 4911, contains rich lanes of dust and gas near its centre. These are silhouetted against glowing newborn star clusters and iridescent pink clouds of hydrogen, the existence of which indicates ongoing star formation.

Hubble has also captured the outer spiral arms of NGC 4911, along with thousands of other galaxies of varying sizes.

The high resolution of Hubble’s cameras, paired with considerably long exposures, made it possible to observe these faint details.

NGC 4911 and other spirals near the centre of the cluster are being transformed by the gravitational tug of their neighbours. In the case of NGC 4911, wispy arcs of the galaxy’s outer spiral arms are being pulled and distorted by forces from a companion galaxy (NGC 4911A), to the upper right.

See the full-size, high-resolution image here (0.7M, new window).

The resultant stripped material will eventually be dispersed throughout the core of the Coma Cluster, where it will fuel the intergalactic populations of stars and star clusters.

The Coma Cluster is home to almost 1,000 galaxies, making it one of the densest collections of galaxies in the nearby universe. It continues to transform galaxies at the present epoch, due to the interactions of close-proximity galaxy systems within the dense cluster. Vigorous star formation is triggered in such collisions.

Galaxies in this cluster are so densely packed that they undergo frequent interactions and collisions. When galaxies of nearly equal masses merge, they form elliptical galaxies. Merging is more likely to occur in the centre of the cluster where the density of galaxies is higher, giving rise to more elliptical galaxies.

This natural-colour Hubble image, which combines data obtained in 2006, 2007, and 2009 from the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys, required 28 hours of exposure time.

Adapted from information issued by NASA / ESA / Hubble Heritage Team (STScI/AURA) / K. Cook (LLNL).

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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.

Galaxy record broken again

A cluster of galaxies nearly 10 billion years old

Though this cluster of galaxies (the red dots) is nearly 10 billion years old, it has a surprisingly modern appearance.

Using NASA’s Spitzer Space Telescope, a Texas A&M University-led team of astronomers has uncovered what may very well be the earliest, most distant cluster of galaxies ever detected.

The group of roughly 60 galaxies, called CLG J02182-05102, is nearly 10 billion years old — born just 4 billion years after the Big Bang.

This follows close on the heals of another distant galaxy cluster discovery.

However, it’s not the size nor the age of the cluster that amazes the team of researchers led by Dr Casey Papovich, an assistant professor in the Texas A&M Department of Physics and Astronomy. Rather, it’s the surprisingly modern appearance of CLG J02182-05102 that has them baffled — a huge, red collection of galaxies typical of only present-day galaxies.

“It’s like we dug an archaeological site in Rome and found pieces of modern Rome amongst the ruins,” explains Papovich.

While its neighbouring galaxies appear vastly smaller and far fainter, Papovich says CLG J02182-05102 stands out as a densely-populated bundle of ancient galaxies. Enormous, red galaxies at the centre contain almost 10 times as many stars as our Milky Way, he notes, combining for a total size which rivals that of the most monstrous galaxies of our nearby Universe.

Before now, Papovich says, such a finding would be considered by many astronomers to be highly unlikely, considering the time frame in which they were found.

“The predictions are that these things should be very rare when the Universe was 4 billion years old, and yet, we found them,” Papovich explains. “Not only did we find them, it looks for all intents and purposes like they had already formed completely and evolved into the large concentrations of galaxies that we see in clusters today.”

Exactly why these particular galaxies are fully formed that early is what Papovich and his collaborators — which include astronomers from NASA’s Jet Propulsion Laboratory at the California Institute of Technology (Caltech) as well as Carnegie Observatories — hope to one day uncover. But for now, studying CLG J02182-05102 could help them and other researchers better understand how galaxies form and cluster in general.

Galaxies with a rock ‘n’ roll lifestyle

Artist's impression of the Spitzer Space Telescope

Artist's impression of the Spitzer Space Telescope

The find resulted from a project initiated two years ago when Papovich and his team observed an area of the sky that could encompasses 250 full Moons, the largest extragalactic survey of space ever made — the Spitzer Wide-area InfraRed Extragalactic (SWIRE) survey.

The team focused on a cosmic region of the survey that previously had been observed by other instruments including Japan’s Subaru telescope on Mauna Kea, Hawaii, and the European Space Agency’s orbiting XMM-Newton telescope.

This, combined with infrared data from the United Kingdom Infrared Telescope — also in Hawaii — and Spitzer’s Public Ultra Deep Sky survey instantly revealed a number of distant galaxies.

It wasn’t until Papovich’s group studied faint light from CLG J02182-05102’s least-dim galaxies that they were able to determine they had found a cluster that contained about 60 galaxies full of old, red stars, at a time when the Universe was only 4 billion years old — about 30 percent of the Universe’s current age of 13.7 billion years.

At that point in time, most other galaxies would still have been forming their very first stars and certainly would not have congregated with other galaxies yet.

In essence, Papovich said the galaxies in CLG J02182-05102 must have subscribed to a rock ‘n’ roll lifestyle: They lived fast and died young. It’s another mystery Papovich hopes to solve through deeper observations, including spectroscopy, with the Hubble Telescope later this year.

“That’s one of the reasons this is so interesting,” he adds. “It seems that they somehow had a premonition they would end up in these big clusters, so that’s another thing we want to find out.”

Adapted from information issued by Texas A&M University / NASA / JPL-Caltech / C. Papovich (Texas A&M University) / Adam Hadhazy.

Galaxy distance record smashed

A cluster of galaxies 9.6 billion light-years away

Astronomers have spotted galaxies 9.6 billion light-years away (circled). The arrows indicate galaxies that are likely located at the same distance, clustered around the centre of the image. The contours indicate X-ray emission coming from the cluster. This false colour image covers an area of the sky about 1/10th the size of the Moon.

A team of astronomers from Germany and Japan has discovered the most distant cluster of galaxies known so far — 9.6 billion light-years away.

The X-ray and infrared observations showed that the cluster hosts predominantly old, massive galaxies, demonstrating that the galaxies must have formed earlier than 9.6 billion years ago, ie. when the universe was still very young.

These and similar observations therefore provide new information not only about early galaxy evolution but also about history of the universe as a whole.

Clusters of galaxies are the largest “building blocks” in the universe. Our galaxy, the Milky Way, is part of the Virgo cluster, comprising some 1,000 to 2,000 galaxies.

By observing galaxies and clusters that are very distant from Earth, astronomers can look back in time, as the galaxies’ light was emitted a long time ago and took millions or billions of light-years to reach the astronomers’ telescopes.

Invisible to the naked eye

Astronomers had to use infrared wavelengths, invisible to the naked eye, because the expansion of the universe — which forces distant galaxies to have large velocities — shifts their light from visible to infrared wavelengths.

The Multi-Object Infrared Camera and Spectrometer (MOIRCS) at the Subaru Telescope detects near-infrared wavelengths, at which the galaxies are most luminous.

“The MOIRCS instrument has an extremely powerful capability of measuring distances to galaxies. This is what made our challenging observation possible,” says Masayuki Tanaka from the University of Tokyo.

The Subaru Observatory

The Japanese Subaru Observatory, located in Hawaii.

“Although we confirmed only several massive galaxies at that distance, there is convincing evidence that the cluster is a real, gravitationally bound cluster.”

That the individual galaxies are indeed held together by gravity is confirmed by observations in a very different wavelength band. The gas between the galaxies in clusters is heated to extreme temperatures and emits light at much shorter wavelengths. The team therefore used the XMM-Newton space observatory to look for this radiation in X-rays.

“Despite the difficulties in collecting X-ray photons … we detected a clear signature of hot gas in the cluster,” explains Alexis Finoguenov from the Max Planck Institute for Extraterrestrial Physics.

Record smashed by 400 million light-years

The combination of these different observations led to the pioneering discovery of the galaxy cluster at a distance of 9.6 billion light-years — some 400 million light-years further into the past than the previously most distant cluster known.

An analysis of the data collected about the individual galaxies shows that the cluster contains already an abundance of evolved, massive galaxies that formed some two billion years earlier.

As the processes for galaxy aging are slow, the presence of these galaxies means the cluster must have come about through the merger of massive galaxy groups, each nourishing its dominant galaxy.

The team is continuing the search for more distant clusters.

Adapted from information issued by MPE /NAOJ / Subaru.