scipsy:

A New View of the Tarantula Nebula (via Chandra)

Huge “Structure” of Satellites Found Orbiting Milky Way — Grouping of galaxies puts cosmology “basically in a shambles,” scientist says.

A huge “structure” of satellite galaxies and star clusters has been found wheeling around the Milky Way, according to a new study.

The discovery surprised scientists, in part because the structure might spell trouble for theories of dark matter, the mysterious, invisible substance that’s thought to make up about 23 percent of the mass in the universe.

The finding is only the latest to question dark matter’s existence—last week, for instance, astronomers announced that they’d failed to detect dark matter in the sun’s neighborhood, even though the substance should be there, according to accepted theory.

In the new study, led by Marcel Pawlowski of the University of Bonn in Germany, astronomers reconstructed the locations of the Milky Way’s known satellites using sources ranging from 20th-century photographic plates to recent images from the Sloan Digital Sky Survey.

The team found that the Milky Way’s roughly 20 companions—including dwarf galaxies and blobs of stars known as globular clusters—are distributed in a tidy plane that orbits at a right angle to our galactic disk.

“This is completely contrary to what we expect from theory,” said study co-authorPavel Kroupa, also of the University of Bonn.

“You should be able to look in any direction and still find some satellite galaxies.” That’s because current models of galaxy formation—which are based on dark matter’s existence—predict that the Milky Way’s companions originally came from many different directions and so should have settled into a more or less spherical distribution.

“The logical implication of this [discovery] is that there is no dark matter,” Kroupa said.

Cosmology in “Shambles”?

According to the standard theory of galaxy formation, dark matter was the gravitational scaffold upon which normal matter coalesced to form galaxies in the early universe.

As larger galaxies such as the Milky Way formed, the theory goes, leftover material amassed into hundreds of smaller satellites spread evenly around their host galaxies.

To explain the odd arrangement of satellites around the Milky Way, the Bonn team proposes that our home galaxy collided with a galactic neighbor about 11 billion years ago, which corresponds with the age of the oldest known satellite dwarf galaxy.

According to this idea, the Milky Way stripped material from the other galaxy, and gravity gathered the debris to form dwarf galaxies and globular clusters, which have remained in a plane around the Milky Way ever since, study leader Pawlowski said.

The team asserts that this model deals a significant blow to dark matter, since it shows that galaxies can form without the theoretical substance.

“It means that we have to completely and utterly rethink cosmology,” Kroupa said. “Cosmology is basically in a shambles now.”

Dark Matter Still Viable

But other astronomers aren’t quite ready to give up on dark matter.

“Although the alignment they find is intriguing, it is very premature to conclude that dark matter is in trouble,” said Ken Rines, of Western Washington University in Bellingham.

“Galaxy formation is a very tricky business. We certainly don’t understand the details, and these details may … explain the alignment that they find,” Rines said.

“Although dark matter may eventually be proven wrong, the alignment of dwarf galaxies is more likely a puzzle than a fatal flaw.”

Sukanya Chakrabarti, an astrophysicist at Florida Atlantic University, is also skeptical that the new study rewrites galaxy formation.

The study team’s galaxy-collision scenario can explain the positions of the satellite dwarf galaxies, she concedes.

But that model doesn’t explain why the satellites act as if they have more mass than can be explained by their visible matter alone—one of the main reasons scientists think dark matter exists.

Any alternative to dark matter “must not only reproduce where the stuff is but what its mass is as well,” Chakrabarti said.

(Related: “Dark Matter Hits the Average Human Once a Minute?”)

Study author Kroupa counters that “this is not a problem, because it has already been demonstrated many times with other data that other theories of gravity—such as MOND—describe galaxies excellently, including the satellite galaxies.”

Short for Modified Newtonian dynamics, MOND is a tweaked version of Newton’s theory of gravity, which proponents say can explain the observed motions of stars and galaxies without resorting to dark matter.

Still, Chakrabarti said, it’s also not surprising that current dark matter simulations can’t explain the Milky Way satellites’ unusual orientation.

While the simulations do a good job of modeling the evolution of large-scale structure in the universe, they’re less reliable when it comes to modeling the scale of individual galaxies, which involves interactions between many more variables, she said.

“If you neglect these things and you’re trying to do a very detailed analysis—like where all the satellite galaxies are distributed—you’re going to come up with some discrepancies,”  Chakrabarti said.

“The current simulations of galaxy formation are incomplete,” she continued, “but that doesn’t imply that dark matter isn’t a viable notion.”

Ker Than, National Geographic News

thescienceofreality:

Eight-Bit Supernova

Image courtesy U. Hwang and J. Laming, CXC/NASA

“Looking straight out of a classic video game, a new “element map” of the supernova remnant Cassiopeia A shows where the different layers of the original star ended up three hundred years after the explosion.

Made with data from NASA’s Chandra X-ray Observatory, the new map suggests that the stellar explosion somehow turned the star inside out. For instance, most of the remnant’s pure iron—an element thought to have been made near the dying star’s core—is now found at the object’s outer edges.”

the-star-stuff:

White Dwarfs

A white dwarf is the remnant of an average-sized star that has passed through the red giant stage of its life. After the star has used up its remaining fuel. At this point the star may expel some of its matter into space, creating a planetary nebula. What remains is the dead core of the star. Nuclear fusion no longer takes place. The core glows because of its residual heat. Eventually the core will radiate all of its heat into space and cool down to become what is known as a black dwarf. White dwarf stars are very dense. Their size is about the same as that of the Earth, but the contain as much mass as the Sun. They are extremely hot, reaching temperatures of over 100,000 degrees.

Illustration By Gary’s TT

the-star-stuff:

10 Billion Earth-Like Planets May Exist in Our Galaxy

About 40 percent of red dwarf stars may have Earth-sized planets orbiting them that have the right conditions for life.

Red dwarfs – which are smaller and cooler than our sun – are extremely common, making up 80 percent of stars in the galaxy. Their ubiquity suggests that there are tens of billions of possible places to look for life beyond Earth, with at least 100 such planets located nearby.

The new estimate comes from a team of astronomers using the European Southern Observatory’s HARPS planet-hunting telescope to look at a sample of 102 nearby red dwarfs over a six-year period. The telescope checked for a characteristic wobble from the star, indicating that at least one planet was tugging on it while orbiting around.

The search found nine planets with between one and 10 Earth masses, including two in the habitable zone, possibly giving them the right temperature to have liquid water. Because red dwarfs don’t produce as much heat as our sun, their habitable zones occur much closer to the star.

Larger planets, about the size of Jupiter, were found around less than 12 percent of red dwarfs, suggesting they are rarer than small rocky worlds.

Astronomers hope to someday build a telescope capable of directly imaging the light from an extrasolar planet and see if they contain the telltale chemicals of life, such as oxygen or methane.

Image: NASA/JPL-Caltech

Record Nine-Planet Star System Discovered?
Alien star likely has more planets than the sun, astronomers say.

A star about 127 light-years from Earth may have even more planets than thesun, which would make the planetary system the most populated yet found.

According to a new study, HD 10180—a sunlike star in the southern constellation Hydrus—may have as many as nine orbiting planets, besting the eight official planets in our solar system.

The star first made headlines in 2010 with the announcement of five confirmed planets and two more planetary candidates.

Now, reanalysis of nearly a decade’s worth of data has not only confirmed the existence of the two possible planets but also uncovered the telltale signals of two additional planets possibly circling the star, bringing the total to nine.

“There certainly is, according to my results, strong evidence that this is the most populous planetary system detected—possibly even richer than the solar system,” said study leader Mikko Tuomi, an astronomer at the University of Hertfordshire in the U.K.

“But the two new planetary signals I report exceed the detection threshold only just.”

Early indications are that both newly detected worlds are super-Earths—planets slightly larger than Earth with rocky surfaces—but more measurements will be needed to confirm their existance.

Scorching Super-Earths

The planetary system around HD 10180 is too far from Earth for us to see directly. 

Instead, astronomers detected the planets by measuring their gravitational tugs on the host star using the High Accuracy Planet Searcher (HARPS) instrument on the European Southern Observatory’s 3.6-meter telescope at La Silla, Chile.

The five established planets are between 12 and 25 times the mass of Earth and are all around the sizes of Uranus or Neptune, meaning the worlds are most likely icy gas giants.

Of the two newly confirmed planets, one is about 65 times the mass of Earth, and it orbits farther beyond the main group. The other planet is a super-Earth 1.3 times the mass of our home world that circles very close to the host star.

The two new, unconfirmed planets also have tight orbits: A planet thought to be 1.9 times the mass of Earth completes its orbit in 10 days, while the other world is likely 5.1 Earth masses with an orbit lasting 68 days.

That means, if the planets do exist, they’d be unlikely candidates to host life.

“They are likely hot planets without dense, gaseous atmospheres, because they are just so close to their star,” Tuomi said.

The astronomer now hopes to take more measurements and verify the planets are really there.

Tuomi also hopes to scan the skies for other crowded planetary systems like HD 10180. (Also see “‘Solar Systems’ Common Across the Galaxy, NASA Probe Hints.”)

“We have only just started to detect planets, and the known exoplanet systems are but a tip of the iceberg,” he said.

“So [our] solar system is only one example among a spectrum of different planetary systems we will find in the near future and [is] definitely not unique.”

The new research on the HD 10180 planetary system appears online this week on the website arXiv.org and has been accepted for publication in the journal Astronomy and Astrophysics.

Andrew Fazekas, National Geographic News