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A map of our galaxy the Milky Way, showing pulsars (red), planetary nebulae (blue), globular clusters (yellow), and the orbits of several stars.
Predicting Andromeda’s Satellites |
Using modified laws of gravity, researchers from Case Western Reserve University and Weizmann Institute of Science closely predicted a key property measured in faint dwarf galaxies that are satellites of the nearby giant spiral galaxy Andromeda.
The predicted property in this study is the velocity dispersion, which is the average velocity of objects within a galaxy relative to each other. Astronomers can use velocity dispersion to determine the accelerations of objects within the galaxy and, roughly, the mass of a galaxy, and vice-versa.
To calculate the velocity dispersion for each dwarf galaxy, the researchers utilized Modified Newtonian Dynamics, MOND for short, which is a hypothesis that attempts to resolve what appears to be an insufficient amount of mass in galaxies needed to support their orbital speeds.
MOND suggests that, under a certain condition, Newton’s law of gravity must be altered. That hypothesis is less widely accepted than the hypothesis that all galaxies contain unseen dark matter that provides needed mass.
“MOND comes out surprisingly well in this new test,” said Stacy McGaugh, astronomy professor at Case Western Reserve. “If we’re right about dark matter, this shouldn’t happen.”
McGaugh teamed with Mordehai Milgrom, the father of MOND and professor of physics and astrophysics at Weizmann Institute in Israel. Their study, “Andromeda Dwarfs in the Light of MOND” will be published in the Astrophysical Journal. continue reading
Hubble Catches a Streak of Stars in Side-On View of Spiral Galaxy |
The Hubble Space Telescope captured a thin, glittering streak of stars in a new view of the spiral galaxy ESO 121-6, which lies in the southern constellation of Pictor (The Painter’s Easel).
Viewed almost exactly side-on, the intricate structure of the swirling arms is hidden, but the full length of the galaxy can be seen — including the intense glow from the central bulge, a dense region of tightly packed young stars sitting at the center of the spiral arms.
Tendrils of dark dust can be seen across the frame, partially obscuring the bright center of the galaxy and continuing out towards the smattering of stars at its edges, where the dust lanes and shapes melt into the inky background. Numerous nearby stars and galaxies are visible as small smudges in the surrounding sky, and the brightest stars are dazzlingly prominent towards the bottom left of the image.
ESO 121-6 is a galaxy with patchy, loosely-wound arms and a relatively faint central bulge. It actually belongs to a group of galaxies, a clump of no more than 50 similar structures all loosely bound to one another by gravity. The Milky Way is also a member of a galactic group, known as the Local Group.
The NASA/ESA Hubble Space Telescope — with a little help from an amateur astronomer — has produced one of the best views yet of nearby spiral galaxy Messier 106. Located a little over 20 million light-years away, practically a neighbour by cosmic standards, Messier 106 is one of the brightest and nearest spiral galaxies to our own.
At its heart, as in most spiral galaxies, is a supermassive black hole, but this one is particularly active. Unlike the black hole at the centre of the Milky Way, which pulls in wisps of gas only occasionally, Messier 106’s black hole is actively gobbling up material. As the gas spirals towards the black hole, it heats up and emits powerful radiation. Part of the emission from the centre of Messier 106 is produced by a process that is somewhat similar to that in a laser — although here the process produces bright microwave radiation.
New Views of Andromeda |
n this new view of the Andromeda galaxy from the Herschel space observatory, cool lanes of forming stars are revealed in the finest detail yet. Herschel is a European Space Agency mission with important NASA participation.
Andromeda, also known as M31, is the nearest major galaxy to our own Milky Way at a distance of 2.5 million light-years, making it an ideal natural laboratory to study star formation and galaxy evolution.
Sensitive to the far-infrared light from cool dust mixed in with the gas, Herschel seeks out clouds of gas where stars are born. The new image reveals some of the very coldest dust in the galaxy — only a few tens of degrees above absolute zero — colored red in this image.
By comparison, warmer regions such as the densely populated central bulge, home to older stars, take on a blue appearance.
Intricate structure is present throughout the 200,000-light-year-wide galaxy with star-formation zones organized in spiral arms and at least five concentric rings, interspersed with dark gaps where star formation is absent.
Andromeda is host to several hundred billion stars. This new image of it clearly shows that many more stars will soon to spark into existence.
Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA’s Herschel Project Office is based at JPL, which contributed mission-enabling technology for two of Herschel’s three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the United States astronomical community.
The Deceptive Appearance of NGC 411 |
Globular clusters are roughly spherical collections of extremely old stars, and around 150 of them are scattered around our galaxy. Hubble is one of the best telescopes for studying these, as its extremely high resolution lets astronomers see individual stars, even in the crowded core. The clusters all look very similar, and in Hubble’s images it can be quite hard to tell them apart — and they all look much like NGC 411, pictured in a new image.
And yet appearances can be deceptive: NGC 411 is in fact not a globular cluster, and its stars are not old. It isn’t even in the Milky Way. NGC 411 is classified as an open cluster located in the Small Magellanic Cloud, a small sister galaxy near our own. Less tightly bound than a globular cluster, the stars in open clusters tend to drift apart over time as they age, whereas globulars have survived for well over 10 billion years of galactic history. NGC 411 is a relative youngster — not much more than a tenth of this age. Far from being a relic of the early years of the universe, the stars in NGC 411 are in fact a fraction of the age of the sun.
The stars in NGC 411 are all roughly the same age, having formed at one time from one cloud of gas. But they are not all the same size. Hubble’s image shows a wide range of colors and brightness in the cluster’s stars; these tell astronomers many facts about the stars, including their mass, temperature and evolutionary phase. Blue stars, for instance, have higher surface temperatures than red ones.
The image is a composite produced from ultraviolet, visible and infrared observations made by Hubble’s Wide Field Camera 3. This filter set lets the telescope “see” colors slightly further beyond red and the violet ends of the spectrum.
Nearby Universe’s ‘Cosmic Fog’ Measured |
Researchers from the Laboratoire Leprince-Ringuet (CNRS/École Polytechnique) have carried out the first measurement of the intensity of the diffuse extragalactic background light in the nearby Universe, a fog of photons that has filled the Universe ever since its formation. Using some of the brightest gamma-ray sources in the southern hemisphere, the study was carried out using measurements performed by the HESS telescope array, located in Namibia and involving CNRS and CEA. The study is complementary to that recently carried out by the Fermi-LAT space observatory. These findings provide new insight into the size of the Universe observable in gamma rays and shed light on the formation of stars and the evolution of galaxies. continue reading
Intergalactic Traffic Jam - Nearby Dwarf Galaxy and Possible Protogalaxy Found |
Peering deep into the dim edges of a distorted pinwheel galaxy in the constellation Ursa Major (the Great Bear), astronomers at Case Western Reserve University and their colleagues have discovered a faint dwarf galaxy and another possible young dwarf caught before it had a chance to form any stars.
Within the faint trails of intergalactic traffic, the researchers also found more evidence pointing to two already known dwarf galaxies as probable forces that pulled the pinwheel-shaped disk galaxy known as M101 out of shape.
M101 is the dominant member in a group of 15 galaxies in Ursa Major. Most galaxies reside in such small-group environments, which means the factors shaping M101 are likely the same shaping most galaxies throughout the universe, the researchers say.
Their efforts, which required the researchers to discern starlight 100 times fainter than the black of the dark night sky and trace extremely low concentrations of interstellar gases among the celestial bodies, are reported in two papers published in the Astrophysical Journal.
“We created the deepest image ever taken of M101 and followed it up with the most sensitive survey of gas clouds surrounding the galaxy,” said Chris Mihos, an astronomy professor at Case Western Reserve and lead author of both papers. “Compared to what is seen in the Hubble Space Telescope image, the galaxy’s disk is much larger and we can see very large, faint plumes of stars and streamers of gas in its outskirts.” continue reading
Massive Supply of Gas Around Modern Galaxies |
Galaxies have a voracious appetite for fuel — in this case, fresh gas — but astronomers have had difficulty finding the pristine gas that should be falling onto galaxies. Now, scientists have provided direct empirical evidence for these gas flows using new observations from the Hubble Space Telescope.
The team led by Nicolas Lehner, research associate professor at the University of Notre Dame, is presenting its work January 11 at the meeting of the American Astronomical Society in Long Beach, Calif.
The team’s observations using Hubble’s two ultraviolet spectrographs, the Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph, show large quantities of cool gas with very low quantities of heavy elements in the gaseous cocoons surrounding modern galaxies. The lack of heavy elements indicates this gas in the circumgalactic medium of the galaxies has not been strongly processed through stars. The members’ work, “The Bimodal Metallicity Distribution of the Cool Circumgalactic Medium at z<1,” has been submitted to the Astrophysical Journal.
Led by Lehner, the team of astronomers identified gaseous streams near galaxies through the absorption they imprint on the spectra of distant, bright background quasars. The atoms in the gas remove small amounts of the light, and as the light from the quasars passes through the gas around galaxies, the chemical elements leave characteristic spectral “fingerprints” that allow astronomers to study the physical and chemical properties of the gas. Lehner and collaborators searched for the signature of gas within about 100,000-300,000 light-years of galaxies, identifying this gas due to its strong hydrogen absorption, a known signature of circumgalactic gas. They subsequently determined the amount of “metals” — all elements heavier than hydrogen and helium — in this gas to test whether the circumgalactic matter was being newly accreted from intergalactic space and lacking in metals or being ejected from the galaxies themselves and strong in metals. continue reading
The Largest-Known Spiral Galaxy |
The spectacular barred spiral galaxy NGC 6872 has ranked among the biggest stellar systems for decades. Now a team of astronomers from the United States, Chile and Brazil has crowned it the largest-known spiral, based on archival data from NASA’s Galaxy Evolution Explorer (GALEX) mission, which has since been loaned to the California Institute of Technology, Pasadena, Calif.
Measuring tip-to-tip across its two outsized spiral arms, NGC 6872 spans more than 522,000 light-years, making it more than five times the size of our Milky Way galaxy.
“Without GALEX’s ability to detect the ultraviolet light of the youngest, hottest stars, we would never have recognized the full extent of this intriguing system,” said lead scientist Rafael Eufrasio, a research assistant at NASA’s Goddard Space Flight Center in Greenbelt, Md., and a doctoral student at Catholic University of America in Washington. He presented the findings January 10 at the American Astronomical Society meeting in Long Beach, Calif.
The galaxy’s unusual size and appearance stem from its interaction with a much smaller disk galaxy named IC 4970, which has only about one-fifth the mass of NGC 6872. The odd couple is located 212 million light-years from Earth in the southern constellation Pavo.
Astronomers think large galaxies, including our own, grew through mergers and acquisitions — assembling over billions of years by absorbing numerous smaller systems. continue reading
