Andromeda Galaxy

The Andromeda Galaxy Could Be Buzzing With Dark Matte

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Roughly 80 percent of the mass of the universe is made up of material that scientists cannot directly observe. Known as dark matter, this bizarre ingredient does not emit light or energy. So why do scientists think it dominates?

Studies of other galaxies in the 1950s first indicated that the universe contained more matter than seen by the naked eye. Support for dark matter has grown, and although no solid direct evidence of dark matter has been detected, there have been strong possibilities in recent years.

The familiar material of the universe, known as baryonic matter, is composed of protons, neutrons and electrons. Dark matter may be made of baryonic or non-baryonic matter. To hold the elements of the universe together, dark matter must make up approximately 80 percent of its matter. [Image Gallery: Dark Matter Across the Universe]

The missing matter could simply be more challenging to detect, made up of regular, baryonic matter. Potential candidates include dim brown dwarfs, white dwarfs and neutrino stars. Supermassive black holes could also be part of the difference. But these hard-to-spot objects would have to play a more dominant role than scientists have observed to make up the missing mass, while other elements suggest that dark matter is more exotic.

These illustrations, taken from computer simulations, show a swarm of dark matter clumps around our Milky Way galaxy. Image released July 10, 2012.
These illustrations, taken from computer simulations, show a swarm of dark matter clumps around our Milky Way galaxy. Image released July 10, 2012.

Most scientists think that dark matter is composed of non-baryonic matter. The lead candidate, WIMPS(weakly interacting massive particles), have ten to a hundred times the mass of a proton, but their weak interactions with “normal” matter make them difficult to detect. Neutralinos, massive hypothetical particles heavier and slower than neutrinos, are the foremost candidate, though they have yet to be spotted. The smaller neutral axion and the uncharched photinos are also potential placeholders for dark matter.

A third possibility exists — that the laws of gravity that have thus far successfully described the motion of objects within the solar system require revision.

Proving the unseen

If scientists can’t see dark matter, how do they know it exists?

Scientists calculate the mass of large objects in space by studying their motion. Astronomers examining spiral galaxies in the 1950s expected to see material in the center moving faster than on the outer edges. Instead, they found the stars in both locations traveled at the same velocity, indicating the galaxies contained more mass than could be seen. Studies of the gas within elliptical galaxies also indicated a need for more mass than found in visible objects. Clusters of galaxies would fly apart if the only mass they contained were visible to conventional astronomical measurements.

Albert Einstein showed that massive objects in the universe bend and distort light, allowing them to be used as lenses. By studying how light is distorted by galaxy clusters, astronomers have been able to create a map of dark matter in the universe.

All of these methods provide a strong indication that the most of the matter in the universe is something yet unseen.

Dark matter versus dark energy

Although dark matter makes up most of the matter of the universe, it only makes up about a quarter of the composition. The universe is dominated by dark energy.

After the Big Bang, the universe began expanding outward. Scientists once thought that it would eventually run out of the energy, slowing down as gravity pulled the objects inside it together. But studies of distant supernovae revealed that the universe today is expanding faster than it was in the past, not slower, indicating that the expansion is accelerating. This would only be possible if the universe contained enough energy to overcome gravity — dark energy.

Source:space.com

Andromeda galaxy scanned with high-energy X-ray vision

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Andromeda galaxy scanned with high-energy X-ray vision
NASA’s Nuclear Spectroscope Telescope Array, or NuSTAR, has imaged a swath of the Andromeda galaxy — the nearest large galaxy to our own Milky Way galaxy. 

NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured the best high-energy X-ray view yet of a portion of our nearest large, neighboring galaxy, Andromeda. The space mission has observed 40 “X-ray binaries”—intense sources of X-rays comprised of a black hole or neutron star that feeds off a stellar companion.

The results will ultimately help researchers better understand the role of X-ray binaries in the evolution of our universe. According to astronomers, these energetic objects may play a critical role in heating the intergalactic bath of gas in which the very first galaxies formed.

“Andromeda is the only large spiral galaxy where we can see individual X-ray binaries and study them in detail in an environment like our own,” said Daniel Wik of NASA Goddard Space Flight Center in Greenbelt, Maryland, who presented the results at the 227th meeting of American Astronomical Society in Kissimmee, Florida. “We can then use this information to deduce what’s going on in more distant galaxies, which are harder to see.”

Andromeda, also known as M31, can be thought of as the big sister to our own Milky Way galaxy. Both galaxies are spiral in shape, but Andromeda is slightly larger than the Milky Way in size. Lying 2.5 million light-years away, Andromeda is relatively nearby in cosmic terms. It can even be seen by the naked eye in dark, clear skies.

Other space missions, such as NASA’s Chandra X-ray Observatory, have obtained crisper images of Andromeda at lower X-ray energies than the high-energy X-rays detected by NuSTAR. The combination of Chandra and NuSTAR provides astronomers with a powerful tool for narrowing in on the nature of the X-ray binaries in spiral galaxies.

In X-ray binaries, one member is always a dead star or remnant formed from the explosion of what was once a star much more massive than the sun. Depending on the mass and other properties of the original giant star, the explosion may produce either a black hole or neutron star. Under the right circumstances, material from the companion star can “spill over” its outermost edges and then be caught by the gravity of the black hole or neutron star. As the material falls in, it is heated to blazingly high temperatures, releasing a huge amount of X-rays.

With NuSTAR’s new view of a swath of Andromeda, Wik and colleagues are working on identifying the fraction of X-ray binaries harboring black holes versus neutron stars. That research will help them understand the population as a whole.

“We have come to realize in the past few years that it is likely the lower-mass remnants of normal stellar evolution, the black holes and neutron stars, may play a crucial role in heating of the intergalactic gas at very early times in the universe, around the cosmic dawn,” said Ann Hornschemeier of NASA Goddard, the principal investigator of the NuSTAR Andromeda studies.

“Observations of local populations of stellar-mass-sized and with NuSTAR allow us to figure out just how much power is coming out from these systems.”

The new research also reveals how Andromeda may differ from our Milky Way. Fiona Harrison, the principal investigator of the NuSTAR mission, added, “Studying the extreme stellar populations in Andromeda tells us about how its history of forming stars may be different than in our neighborhood.”

Harrison will be presenting the 2015 Rossi Prize lecture at the AAS meeting. The prize, awarded by the AAS’s High-Energy Astrophysics Division, honors physicist Bruno Rossi, an authority on cosmic-ray physics and a pioneer in the field of X-ray astronomy.

Milky Way’s Most Distant Stars Spotted.

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Like a boat floating in a vast, empty ocean, a newly discovered star now holds the record as the most distant one in our Milky Way galaxy.

Galaxies are islands of stars spread throughout space, essentially, separated by voids littered with relatively few stars. The newly spotted Milky Way star, dubbed ULAS J0015+01, is a distant red giant that resides a jaw-dropping 900,000 light-years away. The most remarkable thing about the star is that it is still within the gravitational grasp of our own galaxy.

It was spotted along with another cool stellar old-timer named ULAS J0744+25, which is some 775,000  light-years away, by a team led by John Bochanski of Haverford College in Haverford, Pennsylvania.

The two stars are more than 50 percent farther from the sun than any known star in the Milky Way, or about five times more distant than the Large Magellanic Cloud, a dwarf galaxy that circles our galaxy. In fact, the two stars lie about one third of the distance to the Andromeda galaxy, the Milky Way’s sister spiral in the Local Group of nearby galaxies.

“The distances to these two stars are almost too large to comprehend,” says Bochanski. “To put it in perspective, when the light from ULAS J0015+01 left the star, our early human ancestors were just starting to make fires here on Earth.”

The feeble light from both red giants were picked up by the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey.

It’s a pretty lonely place beyond the Milky Way’s halo. Only seven stars having been cataloged to date that lie beyond the 400,000 light-year halo of stars that cocoon our galaxy.

But beyond the extreme records, these distant stars interest astronomers because they call the Milky Way’s extended halo their home. As far-flung outliers from the galaxy, they may shed light on its origin and evolution. Current theories point to our galaxy colliding with many smaller dwarf galaxies in the distant past, resulting in small smatterings of stars thrown out into intergalactic space. Both ULAS J0744+25 and ULAS J0015+01 may in fact be all that is left over of one such ancient collision.

See for Yourself

Okay, so while these stars are only visible with world-class telescopes, what about the most distant star visible to the naked eye?

If we are talking in terms of the brightest, most distant star then that would be Deneb, the lead star in the summertime constellation Cygnus. Despite having an estimated average distance of 1,400 light-years away, Deneb shines as one of the brightest stars in the heavens.

This sky-chart shows the location of Deneb, the lead star in the constellation Cygnus. Credit: SkySafari
This sky chart shows the location of Deneb, the lead star in the constellation Cygnus. Credit: SkySafari

It is easy to find at this time of the year for those in the Northern Hemisphere, since it lies overhead during late nights and pins down one of the corners of the Summer Triangle stellar pattern.

But the record as the farthest star we can see with the naked eye would probably have to go to Rho Cassiopeiae—at an astounding 8,000 light-years from Earth. That is 472,000 trillion miles (760,000 trillion kilometers) away.

This skychart shows the constellation Cassiopeia in the northeast evening sky, home to Rho Cass - the most distant star the unaided human eye can see. Credit: SkySfari
This sky chart shows the constellation Cassiopeia in the northeast evening sky, home to Rho Cass, the most distant star the unaided human eye can see. Credit: SkySfari

Shining at magnitude +4.5,  it is just visible as a very faint star from the countryside or darker suburbs. The star glints from within the W- or M-shaped (depending on season) constellation Cassiopeia, the Queen. It can be seen throughout the year from mid-northern latitude locations, always in the general vicinity of the North Star.

The reason we can actually see Rho Cass is because it is classified as a hypergiant star, one that has a diameter some 500 times wider than our own sun, which it outshines 10,000 times more brightly. Astronomers believe this makes for an explosive combination and so computer models are suggesting that this stellar monster may explode as a supernovae anytime.

So, try and catch it while you can.

Hubble Zooms in On Double Nucleus in Andromeda Galaxy.

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A new Hubble Space Telescope image centers on the 100-million-solar-mass black hole at the hub of the neighboring spiral galaxy M31, or the Andromeda galaxy, the only galaxy outside the Milky Way visible to the naked eye and the only other giant galaxy in the local group.

This is the sharpest visible-light image ever made of the nucleus of an external galaxy.

The event horizon, the closest region around the black hole where light can still escape, is too small to be seen, but it lies near the middle of a compact cluster of blue stars at the center of the image. The compact cluster of blue stars is surrounded by the larger “double nucleus” of M31, discovered with the Hubble Space Telescope in 1992. The double nucleus is actually an elliptical ring of old reddish stars in orbit around the black hole but more distant than the blue stars. When the stars are at the farthest point in their orbit they move slower, like cars on a crowded freeway. This gives the illusion of a second nucleus.

The blue stars surrounding the black hole are no more than 200 million years old, and therefore must have formed near the black hole in an abrupt burst of star formation. Massive blue stars are so short-lived that they would not have enough time to migrate to the black hole if they were formed elsewhere.

Astronomers are trying to understand how apparently young stars were formed so deep inside the black hole’s gravitational grip and how they survive in an extreme environment.

The fact that young stars are also closely bound to the central black hole in our Milky Way galaxy suggests this may be a common phenomenon in spiral galaxies.

Tod R. Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., assembled this image of the nuclear region by taking several blue and ultraviolet light exposures of the nucleus with Hubble’s Advanced Camera for Surveys high-resolution channel, each time slightly moving the telescope to change how the camera sampled the region. By combining these pictures, he was able to construct an ultra-sharp view of the galaxy’s core.

Lauer is presenting these Hubble observations this week at the meeting of the American Astronomical Society in Austin, Texas.

 

Source: http://www.sciencedaily.com