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Hubble Catches a Stellar Exodus in Action

Astronomy News - 15 May 2015 - 10:23am

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Globular star clusters are isolated star cities, home to hundreds of thousands of stars. And like the fast pace of cities, there's plenty of action in these stellar metropolises. The stars are in constant motion, orbiting around the cluster's center. Past observations have shown that the heavyweight stars live in the crowded downtown, or core, and lightweight stars reside in the less populated suburbs.

Galaxies die by slow 'strangulation'

Astronomy News - 15 May 2015 - 10:06am

A study suggests that when most galaxies stop forming stars, this death is a slow process that gradually chokes them of the necessary cool gases.

The Dark Side of Star Clusters

Astronomy News - 14 May 2015 - 10:17am
Observations with ESO’s Very Large Telescope in Chile have discovered a new class of “dark” globular star clusters around the giant galaxy Centaurus A. These mysterious objects look similar to normal clusters, but contain much more mass and may either harbour unexpected amounts of dark matter, or contain massive black holes — neither of which was expected nor is understood.

Corkscrew planets spiral back and forth between two stars

Astronomy News - 14 May 2015 - 10:16am
In some rare cases, a planet in a binary system may spiral around the axis that connects its two stars – although how such planets come to be is unclear

Found: giant spirals in space that could explain our existence

Astronomy News - 14 May 2015 - 10:16am

Why there is any matter at all is one of physics' biggest mysteries. Hints of a spiralled intergalactic magnetic field could solve it

Strangulation as the primary mechanism for shutting down star formation in galaxies

Astronomy News - 14 May 2015 - 10:15am

Strangulation as the primary mechanism for shutting down star formation in galaxies

Nature 521, 7551 (2015). doi:10.1038/nature14439

Authors: Y. Peng, R. Maiolino & R. Cochrane

Local galaxies are broadly divided into two main classes, star-forming (gas-rich) and quiescent (passive and gas-poor). The primary mechanism responsible for quenching star formation in galaxies and transforming them into quiescent and passive systems is still unclear. Sudden removal of gas through outflows or stripping is one of the mechanisms often proposed. An alternative mechanism is so-called “strangulation”, in which the supply of cold gas to the galaxy is halted. Here we report an analysis of the stellar metallicity (the fraction of elements heavier than helium in stellar atmospheres) in local galaxies, from 26,000 spectra, that clearly reveals that strangulation is the primary mechanism responsible for quenching star formation, with a typical timescale of four billion years, at least for local galaxies with a stellar mass less than 1011 solar masses. This result is further supported independently by the stellar age difference between quiescent and star-forming galaxies, which indicates that quiescent galaxies of less than 1011 solar masses are on average observed four billion years after quenching due to strangulation.

Cause of galactic death: strangulation

Astronomy News - 14 May 2015 - 10:13am

As murder mysteries go, it’s a big one: how do galaxies die and what kills them? A new study, published today in the journal Nature, has found that the primary cause of galactic death is strangulation, which occurs after galaxies are cut off from the raw materials needed to make new stars.

Researchers from the University of Cambridge and the Royal Observatory Edinburgh have found that levels of metals contained in dead galaxies provide key ‘fingerprints’, making it possible to determine the cause of death.

There are two types of galaxies in the Universe: roughly half are ‘alive’ galaxies which produce stars, and the other half are ‘dead’ ones which don’t. Alive galaxies such as our own Milky Way are rich in the cold gas – mostly hydrogen – needed to produce new stars, while dead galaxies have very low supplies. What had been unknown is what’s responsible for killing the dead ones.

Astronomers have come up with two main hypotheses for galactic death: either the cold gas needed to produce new stars is suddenly ‘sucked’ out of the galaxies by internal or external forces, or the supply of incoming cold gas is somehow stopped, slowly strangling the galaxy to death over a prolonged period of time.

In order to get to the bottom of this mystery, the team used data from the Sloan Digital Sky Survey to analyse metal levels in more than 26,000 average-sized galaxies located in our corner of the universe.

“Metals are a powerful tracer of the history of star formation: the more stars that are formed by a galaxy, the more metal content you’ll see,” said Dr Yingjie Peng of Cambridge’s Cavendish Laboratory and Kavli Institute of Cosmology, and the paper’s lead author. “So looking at levels of metals in dead galaxies should be able to tell us how they died.”

If galaxies are killed by outflows suddenly pulling the cold gas out of the galaxies, then the metal content of a dead galaxy should be the same as just before it died, as star formation would abruptly stop.

In the case of death by strangulation however, the metal content of the galaxy would keep rising and eventually stop, as star formation could continue until the existing cold gas gets completely used up.

While it is not possible to analyse individual galaxies due to the massive timescales involved, by statistically investigating the difference of metal content of alive and dead galaxies, the researchers were able to determine the cause of death for most galaxies of average size.

“We found that for a given stellar mass, the metal content of a dead galaxy is significantly higher than a star-forming galaxy of similar mass,” said Professor Roberto Maiolino, co-author of the new study. “This isn’t what we’d expect to see in the case of sudden gas removal, but it is consistent with the strangulation scenario.”

The researchers were then able to independently test their results by looking at the stellar age difference between star-forming and dead galaxies, independent of metal levels, and found an average age difference of four billion years – this is in agreement with the time it would take for a star-forming galaxy to be strangled to death, as inferred from the metallicity analysis.

“This is the first conclusive evidence that galaxies are being strangled to death,” said Peng. “What’s next though, is figuring out what’s causing it. In essence, we know the cause of death, but we don’t yet know who the murderer is, although there are a few suspects.” 

Astronomers have partially solved an epic whodunit: what kills galaxies so that they can no longer produce new stars?

This is the first conclusive evidence that galaxies are being strangled to deathYingjie Pengre-activeArtist’s impression of one of the possible galaxy strangulation mechanisms: star-forming galaxies (fed by gas inflows) are accreted into a massive hot halo, which ‘strangles’ them and leads to their death.

The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.


Watch this animation introducing significant moments in our understanding of lig...

Astronomy News - 14 May 2015 - 10:12am
Watch this animation introducing significant moments in our understanding of light!

Produced by The Open University with funding from the RAS and SEPnet, to celebrate the International Year of Light 2015

International Year of Light

Learn more about the International Year of Light from The Open University --- DES...

Astrophysics: The slow death of red galaxies

Astronomy News - 14 May 2015 - 10:10am

Astrophysics: The slow death of red galaxies

Nature 521, 7551 (2015). doi:10.1038/521164a

Authors: Andrea Cattaneo

For most galaxies, the shutdown of star formation was a slow process that took 4 billion years. An analysis of some 27,000 galaxies suggests that 'strangulation' by their environment was the most likely cause. See Letter p.192

Microwave oven blamed for radio-telescope signals

Astronomy News - 14 May 2015 - 10:08am

Microwave oven blamed for radio-telescope signals

Nature 521, 7551 (2015). doi:10.1038/521129f

Author: Chris Woolston

Studies about mysterious signals and super-strong spider silk triggered online chatter.

Astrophysics: Farthest galaxy measured

Astronomy News - 14 May 2015 - 10:08am

Astrophysics: Farthest galaxy measured

Nature 521, 7551 (2015). doi:10.1038/521129b

Astronomers have observed a distant galaxy as it looked just 650 million years after the Big Bang, making it the farthest galaxy to have its distance reliably measured.Pascal Oesch at Yale University in New Haven, Connecticut, and his colleagues used a telescope at the

Probe spies Pluto's faint moons

Astronomy News - 14 May 2015 - 9:52am

The New Horizons probe, heading for its historic flyby of Pluto in July, has now caught sight of all the known faint moons of the dwarf planet.

NASA Research Reveals Europa's Mystery Dark Material Could Be Sea Salt

Astronomy News - 13 May 2015 - 10:13am
NASA experiments suggest the dark material coating some geological features of Jupiter's moon Europa is likely sea salt from a subsurface ocean, discolored by exposure to radiation. Sea salt on Europa's surface suggests the ocean is interacting with its seafloor - an important consideration in determining whether the icy moon could support life.

Mars volcanoes launch dust storms like a skate ramp

Astronomy News - 13 May 2015 - 10:12am
Weird dust storms on Mars suggest that massive volcano Olympus Mons is the solar system's sickest half-pipe

The election results are in: the next President of the RAS will be Prof. John Za...

Astronomy News - 12 May 2015 - 10:31am
The election results are in: the next President of the RAS will be Prof. John Zarnecki!

New vice-presidents are Don Kurtz and Christine Peirce, whilst new Councillors are Joanna Barstow, Mike Bode, Caitriona Jackman, Sara Russell and Stephen Serjeant.

Election results 2015: new President and Council
The results of the 2015 RAS elections were announced at the Annual General Meeting of the society on 8 May. The following Fellows were elected to serve on Council, the governing body of the society:

Auroras on Mars

Astronomy News - 12 May 2015 - 10:31am
NASA's MAVEN spacecraft has detected widespread auroras on Mars.

Millions of missing galaxies found hiding in plain sight

Astronomy News - 12 May 2015 - 10:30am

A type of galaxy thought to be all but extinct has turned up in our own backyard in the same abundance as in the early universe

Supernova blast shows stars die in lopsided explosions

Astronomy News - 11 May 2015 - 10:08am

A closer look at a supernova confirms simulations that an asymmetric explosion is required to trigger stellar death

Hubble Finds Giant Halo Around the Andromeda Galaxy

Astronomy News - 8 May 2015 - 10:08am

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The Andromeda galaxy is our Milky Way's nearest neighbor in space. The majestic spiral of over 100 billion stars is comparable in size to our home galaxy. At a distance of 2.5 million light-years, it is so close to us the galaxy can be seen as a cigar-shaped smudge of light high in the autumn sky. But if you could see the huge bubble of hot, diffuse plasma surrounding it, it would appear 100 times the angular diameter of the full Moon! The gargantuan halo is estimated to contain half the mass of the stars in the Andromeda galaxy itself. It can be thought of as the "atmosphere" of a galaxy. Astronomers using Hubble identified the gas in Andromeda's halo by measuring how it filtered the light of distant bright background objects called quasars. It is akin to seeing the glow of a flashlight shining through a fog. This finding promises to tell astronomers more about the evolution and structure of one of the most common types of galaxies in the universe.

Mercury's magnetic heart was beating soon after its birth

Astronomy News - 8 May 2015 - 10:07am
The planet's molten core became magnetic nearly 4 billion years ago – potentially making Mercury's magnetic field the most enduring in our solar system