Tag: hydrogen gas (page 1 of 2)

Mysterious Galaxy X Found Finally? Dark Matter Hunters Would Like To Believe So

Excerpt from techtimes.comAstronomers have long suspected strange ripples in hydrogen gas in the disk of our Milky Way galaxy are caused by the gravity of an unseen dwarf galaxy dominated by dark matter -- and now they think they've found this "Gal...

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Planck telescope puts new datestamp on first stars


Polarisation of the sky
Planck has mapped the delicate polarisation of the CMB across the entire sky



Excerpt from bbc.com

Scientists working on Europe's Planck satellite say the first stars lit up the Universe later than previously thought.

The team has made the most precise map of the "oldest light" in the cosmos.

Earlier observations of this radiation had suggested the first generation of stars were bursting into life by about 420 million years after the Big Bang.

Planck's data indicates this great ignition was well established by some 560 million years after it all began.

"This difference of 140 million years might not seem that significant in the context of the 13.8-billion-year history of the cosmos, but proportionately it's actually a very big change in our understanding of how certain key events progressed at the earliest epochs," said Prof George Efstathiou, one of the leaders of the Planck Science Collaboration.

Subtle signal

The assessment is based on studies of the "afterglow" of the Big Bang, the ancient light called the Cosmic Microwave Background (CMB), which still washes over the Earth today.
Prof George Efstathiou: "We don't need more complicated explanations"

The European Space Agency's (Esa) Planck satellite mapped this "fossil" between 2009 and 2013.

It contains a wealth of information about early conditions in the Universe, and can even be used to work out its age, shape and do an inventory of its contents.

Scientists can also probe it for very subtle "distortions" that tell them about any interactions the CMB has had on its way to us.

Forging elements

One of these would have been imprinted when the infant cosmos underwent a major environmental change known as re-ionisation.

Prof Richard McMahon: "The two sides of the bridge now join"
It is when the cooling neutral hydrogen gas that dominated the Universe in the aftermath of the Big Bang was then re-energised by the ignition of the first stars.

These hot giants would have burnt brilliant but brief lives, producing the very first heavy elements. But they would also have "fried" the neutral gas around them - ripping electrons off the hydrogen protons.

And it is the passage of the CMB through this maze of electrons and protons that would have resulted in it picking up a subtle polarisation.

ImpressionImpression: The first stars would have been unwieldy behemoths that burnt brief but brilliant lives


The Planck team has now analysed this polarisation in fine detail and determined it to have been generated at 560 million years after the Big Bang.

The American satellite WMAP, which operated in the 2000s, made the previous best estimate for the peak of re-ionisation at 420 million years. 

The problem with that number was that it sat at odds with Hubble Space Telescope observations of the early Universe.

Hubble could not find stars and galaxies in sufficient numbers to deliver the scale of environmental change at the time when WMAP suggested it was occurring.

Planck's new timing "effectively solves the conflict," commented Prof Richard McMahon from Cambridge University, UK.

"We had two groups of astronomers who were basically working on different sides of the problem. The Planck people came at it from the Big Bang side, while those of us who work on galaxies came at it from the 'now side'. 

"It's like a bridge being built over a river. The two sides do now join where previously we had a gap," he told BBC News.

That gap had prompted scientists to invoke complicated scenarios to initiate re-ionisation, including the possibility that there might have been an even earlier population of giant stars or energetic black holes. Such solutions are no longer needed.

No-one knows the exact timing of the very first individual stars. All Planck does is tell us when large numbers of these stars had gathered into galaxies of sufficient strength to alter the cosmic environment. 

By definition, this puts the ignition of the "founding stars" well before 560 million years after the Big Bang. Quite how far back in time, though, is uncertain. Perhaps, it was as early as 200 million years. It will be the job of the next generation of observatories like Hubble's successor, the James Webb Space Telescope, to try to find the answer.

JWSTBeing built now: The James Webb telescope will conduct a survey of the first galaxies and their stars
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The history of the Universe

Graphic of the history of time
  • Planck's CMB studies indicate the Big Bang was 13.8bn years ago
  • The CMB itself can be thought of as the 'afterglow' of the Big Bang
  • It spreads across the cosmos some 380,000 years after the Big Bang
  • This is when the conditions cool to make neutral hydrogen atoms
  • The period before the first stars is often called the 'Dark Ages'
  • When the first stars ignite, they 'fry' the neutral gas around them
  • These giants also forge the first heavy elements in big explosions
  • 'First Light', or 'Cosmic Renaissance', is a key epoch in history
line

The new Planck result is contained in a raft of new papers just posted on the Esa website. 

These papers accompany the latest data release from the satellite that can now be used by the wider scientific community, not just collaboration members.
Dr Andrew Jaffe: "The simplest models for inflation are ruled out"
Two years ago, the data dump largely concerned interpretations of the CMB based on its temperature profile. It is the CMB's polarisation features that take centre-stage this time.
It was hoped that Planck might find direct evidence in the CMB's polarisation for inflation - the super-rapid expansion of space thought to have occurred just fractions of a second after the Big Bang. This has not been possible. But all the Planck data - temperature and polarisation information - is consistent with that theory, and the precision measurements mean new, tighter constraints have been put on the likely scale of the inflation signal, which other experiments continue to chase.
What is clear from the Planck investigation is that the simplest models for how the super-rapid expansion might have worked are probably no longer tenable, suggesting some exotic physics will eventually be needed to explain it.
"We're now being pushed into a parameter space we didn't expect to be in," said collaboration scientist Dr Andrew Jaffe from Imperial College, UK. "That's OK. We like interesting physics; that's why we're physicists, so there's no problem with that. It's just we had this naïve expectation that the simplest answer would be right, and sometimes it just isn't."

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‘G2’ Gas Ball Survives Black Hole, and Researchers Say They Now Know Why

Excerpt from sciencetimes.com  For years, astronomers have pondered the origins and the contents of the mysterious G2 object floating in the center of the Milky Way galaxy. Drifting towards the galaxy's supermassive black hole, the passing ...

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Our Milky Way strips nearby galaxies of star-forming hydrogen


 Artist's impression of the Milky Way. Its hot halo appears to be stripping away the star-forming atomic hydrogen from its companion dwarf spheroidal galaxies.  Image credit: NRAO/AUI/NSF
Artist’s impression of the Milky Way. Its hot halo appears to be stripping away the star-forming atomic hydrogen from its companion dwarf spheroidal galaxies. Image credit: NRAO/AUI/NSF

Excerpt from
earthsky.org

Astronomers have discovered that our nearest galactic neighbors are devoid of star-forming gas, and that our Milky Way is to blame.

New observations by large radio telescopes reveal that within a well-defined boundary around our galaxy, dwarf galaxies are completely devoid of hydrogen gas. Beyond this point, dwarf galaxies are teeming with star-forming material. 

The Milky Way galaxy is actually the largest member of a compact clutch of galaxies that are bound together by gravity. Swarming around our home galaxy is a menagerie of smaller dwarf galaxies, the smallest of which are the relatively nearby dwarf spheroidals, which may be the leftover building blocks of galaxy formation.

Further out are a number of similarly sized and slightly misshaped dwarf irregular galaxies, which are not gravitationally bound to the Milky Way and may be relative newcomers to our galactic neighborhood.

Kristine Spekkens is an assistant professor at the Royal Military College of Canada and lead author on a paper published in the Astrophysical Journal Letters. She said:
"Astronomers wondered if, after billions of years of interaction, the nearby dwarf spheroidal galaxies have all the same star-forming ‘stuff’ that we find in more distant dwarf galaxies."

Previous studies have shown that the more distant dwarf irregular galaxies have large reservoirs of neutral hydrogen gas, the fuel for star formation. These past observations, however, were not sensitive enough to rule out the presence of this gas in the smallest dwarf spheroidal galaxies. 

Spekkens said:
"What we found is that there is a clear break, a point near our home galaxy where dwarf galaxies are completely devoid of any traces of neutral atomic hydrogen."
 Bottom line: New observations by large radio telescopes reveal that within a well-defined boundary around our galaxy, dwarf galaxies are completely devoid of star-making hydrogen gas. Astronomers say our Milky Way is to blame.

Known Milky Way satellite galaxies.  Click here for more about this diagram.
Neighboring galaxies to our own Milky Way (Descriptions below)
 

NAME DISTANCE (kpc) DISCOVERY PAPER
Canes Major 7.2Martin et al. 2004, A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion on to the Milky Way
Segue 317 Belokurov et al. 2010, Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way
Segue 123 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Sagittarius24Ibata, Gilmore & Irwin, 1994, A dwarf satellite galaxy in Sagittarius 1995, Sagittarius: the nearest dwarf galaxy
Segue 234.7 Belokurov et al. 2009, The discovery of Segue 2: a prototype of the population of satellitesof satellites
Bootes II 43 Walsh, Jerjen & Willman, 2007, A Pair of Bootes: A New Milky Way Satellite
Coma 44 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Willman 1 (SDSSJ1049+5103) 45Willman et al. 2005, A New Milky Way Companion: Unusual Globular Cluster or Extreme Dwarf Satellite?
Bootes III 46Grillmair 2009, Four New Stellar Debris Streams in the Galactic Halo
LMC 50.8-
SMC 59.7-
Bootes 60 Belokurov et al. 2006, A Faint New Milky Way Satellite in Bootes
Ursa Minor 66A.G. Wilson of the Lowell Observatory in 1955, Sculptor-Type Systems in the Local Group of Galaxies
Sculptor (Scl) 79discovered in 1938 by Harlow Shapley, A Stellar System of a New Type
Draco 82 A.G. Wilson of the Lowell Observatory in 1955, Sculptor-Type Systems in the Local Group of Galaxies
Sextans 89 Mike Irwin, M.T. Bridgeland, P.S. Bunclark and R.G. McMahon, 1990 A new satellite galaxy of the Milky Way in the constellation of Sextans
Ursa Major (UMa) 100Willman et al. 2005, A New Milky Way Dwarf Galaxy in Ursa Major
Carina 103Cannon, R. D., Hawarden, T. G., & Tritton, S. B., 1977, A new Sculptor-type dwarf elliptical galaxy in Carina
Hercules 140 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Fornax 140discovered in 1938 by Harlow Shapley, described in "Two Stellar Systems of a New Kind", Nature, Vol. 142, p. 715
Canes Venatici II 150 Sakamoto & Hasegawa 2006, Discovery of a Faint Old Stellar System at 150 kpc
Leo IV 160 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Pisces II 182 Belokurov et al. 2010, Big Fish, Little Fish: Two New Ultra-Faint Satellites of The Milky Way
Leo II (Leo B) 208 Robert G. Harrington and Albert George Wilson, 1950, Two New Stellar Systems in Leo
Canes Venatici 220Zucker et al. 2006 A New Milky Way Dwarf Satellite in Canes Venatici
Leo I 254 Robert G. Harrington and Albert George Wilson, 1950, Two New Stellar Systems in Leo

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