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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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Bursting ‘bubbles’ give our Galaxy gas

The regions of our Galaxy the researchers studied

The regions of our Galaxy the researchers studied. More gas clouds were found in the region on the right than in the region on the left.

  • 650 Milky Way gas clouds studied
  • Each contains 700 times the mass of the Sun
  • Clouds might recycle gas in and out of the Galaxy

Like bubbles bursting on the surface of a glass of champagne, ‘bubbles’ in our Galaxy burst and leave ‘flecks’ of material in the form of clouds of hydrogen gas, researchers using CSIRO’s Parkes telescope have found.

Their study explains the origin of these clouds for the first time.

Swinburne University PhD student Alyson Ford (now at the University of Michigan) and her supervisors; Dr Naomi McClure-Griffiths (CSIRO Astronomy and Space Science) and Felix Lockman (US National Radio Astronomy Observatory), have made the first detailed observations of ‘halo’ gas clouds in our Galaxy.

Just as Earth has an atmosphere, the main starry disc of our Galaxy is surrounded by a thinner halo of stars, gas and ‘dark matter’.

The Parkes radio telescope

The Parkes radio telescope

The halo clouds skim the surface of our Galaxy, sitting 400 to 10,000 light-years outside the Galactic disc. They are big — an average-sized cloud contains hydrogen gas 700 times the mass of the Sun and is about 200 light-years across.

“We’re studying the clouds to understand what role they play in recycling material between the disc and halo,” Dr McClure-Griffiths said.

“The clouds can fall back down into the main body of the Galaxy, returning gas to it.”

Gas is “spritzing” up our Galaxy

The researchers studied about 650 clouds and found striking differences between them in different areas of the Galaxy. One part of the Galaxy had three times as many clouds as another next to it, and the clouds were twice as thick.

The region with lots of thick clouds is where lots of stars form, while the region with fewer clouds also forms fewer stars.

An image made with the Parkes radio telescope of some of the 'halo clouds' above the main body of our Galaxy.

An image made with the Parkes radio telescope of some of the 'halo clouds' above the main body of our Galaxy.

But the halo clouds aren’t found exactly where stars are forming right now. Instead, they seem to be linked to earlier star formation.

Massive stars grow old quickly. After a few million years they shed material into space as a ’wind‘ and then explode.

This violence creates bubbles in the gas in space, like the holes in a Swiss cheese.

“Stellar winds and explosions sweep up gas from the Galactic disc into the lower halo.

“We’ve found this churned-up gas is ‘spritzing’ the surface of the Galactic disc in the form of halo clouds.”

A star-forming region is active for less than a million years, but a super-bubble in the Galaxy takes 20 or 30 million years to form.

“Just as yeast takes a while to make wine bubbly, stars take a while to make the Galaxy bubbly,” Dr McClure-Griffiths said.

The halo clouds are distinct from a larger population of ‘high-velocity clouds’ that also sail outside the galaxy. The halo clouds move in tandem with the rotating Galaxy, while the high-velocity clouds scud along much faster.

This study is the first to accurately locate the halo clouds in relation to the main body of the Galaxy. Its findings were presented overnight at a news conference at a meeting of the American Astronomical Society in Miami, Florida.

Adapted from information issued by CSIRO / A Ford (U. Michigan), N. McClure-Griffiths (CSIRO Astronomy and Space Science) / NASA / JPL-Caltech / David McClenaghan.

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.