ikenbot:

New Research Confirms The Existence of Dark Matter

Image: Don Dixon

Fans of dark matter can rest easy. A study published last month raised eyebrows by suggesting that our cosmic neighbourhood is empty of the extra mass needed to hold the galaxy together. But a re-analysis shows that the dark matter was there all along.

Dark matter is the mysterious, invisible stuff that makes up 83 per cent of the matter in the universe. It is responsible for keeping galaxies from flying apart despite their high spinning speeds, and has aided our understanding of how structures in the universe formed.

The most popular theories say that dark matter is a hitherto undetected particle called a WIMP (weakly interacting massive particle) that is shy of interacting with ordinary matter through any force except gravity.

But several underground detectors waiting for WIMPs have come up empty, or with conflicting results. If the galaxy is so full of dark matter, why hasn’t it shown up yet?

In April, a team led by Christian Moni-Bidin of the University of Concepcion in Chile thought they had a solution: the WIMPs aren’t actually there.

The team tracked the motions of more than 400 stars within 13,000 light years of Earth to estimate the mass of matter – visible and dark – in the sun’s local neighbourhood. They concluded that the mass they found could be explained by the visible matter alone, with no need for dark matter.

But the team made a subtle error, say Jo Bovy and Scott Tremaine of the Institute for Advanced Study in Princeton, New Jersey.

Moni-Bidin and colleagues considered stars whose orbits take them far above or below the Milky Way’s main bright disc, and used the speed at which they orbit the centre of the galaxy to figure out how much of a pull they feel from the nearby mass of stars and dark matter. They assumed that the stars’ speeds would be the same no matter how far they were from the galactic centre. Observations of dust clumps have shown that this assumption is true for young stars orbiting in the galactic disc, which mostly move in a near-perfect circle.

But the stars that orbit high above or far below the disc can’t have circular orbits, Bovy says. The only stars that reach such great heights have been kicked away from the disc by matter in the galaxy’s spiral arms, which sent them on highly elliptical orbits.

Full Article: Crisis averted: Dark matter was there all along

ikenbot:

IC 4603

The Turbulent Heart of the Rho Ophiuchi Complex

Copyright: Rolf Wahl Olsen

This image shows the core region of the Rho Ophiuchi Complex, centered around the prominent blue reflection nebula IC 4603. This is one of the nearest star forming regions and the intricacies of the dense interstellar dust clouds in the area provides a spectacular display of light and colours.

The bright star is 7.9 magnitude SAO184376 which is the main source of light for the blue reflection nebula. The contrasting red areas towards the top are primarily due to reflected light from the hearby red giant star Antares, which lies outside the field of view. The entire area is also littered with hundreds of dim reddish stars, which are typically very young T Tauri stars.

ikenbot:

Scorpius in Red and Blue

the-star-stuff:

How alcohol is formed naturally in space

The Sagittarius B2 cloud has ten billion, billion, billion liters of alcohol floating in it. Most of it is undrinkable, but there are some of them are ethanol, which is drinkable by humans. Scientists still don’t know for sure why the booze is out there, but they have a theory.

Top Image: NASA/CXC/Penn State/L. Townsley et al.

Via BBC, Lab News, The Joint Astronomy Center, Ars Technica.

the-star-stuff:

Three-telescope interferometry allows astrophysicists to observe how black holes are fueled

Scientists were able to detect a ring of hot dust that marks the transition from a more distant mixture of gas and dust in a doughnut-shaped structure to a gaseous disk closer to the black hole. By University of California, Santa Barbara — Published: May 17, 2012

Imaged Above: Artist’s view of a dust torus surrounding the accretion disk and the central black hole in active galactic nuclei. Credit: NASA E/PO - Sonoma State University, Aurore Simonnet

ikenbot:

GALEX presents The Andromeda Galaxy

A mere 2.5 million light-years away, the Andromeda Galaxy really is just next door as large galaxy’s go.

So close, and spanning some 260,000 light-years, it took 11 different image fields from the Galaxy Evolution Explorer (GALEX) satellite’s telescope to produce this gorgeous portrait of the spiral galaxy in ultraviolet light.

While its spiral arms stand out in visible light images of Andromeda (also known as M31), the arms look more like rings in the GALEX ultraviolet view, dominated by hot, young, massive stars.

As sites of intense star formation, the rings have been interpreted has evidence Andromeda collided with its smaller neighboring elliptical galaxy M32 more than 200 million years ago. The large Andromeda galaxy and our own Milky Way are the dominant members of the local galaxy group.

expose-the-light:

Top Ten Mysteries of the Universe

What are those burning questions about the cosmos that still baffle astronomers today?

1. What Are Fermi Bubbles?

No, this is not a rare digestive disorder. The bubbles are massive, mysterious structures that emanate from the Milky Ways center and extend roughly 20,000 light-years above and below the galactic plane. The strange phenomenon, first discovered in 2010, is made up of super-high-energy gamma-ray and X-ray emissions, invisible to the naked eye. Scientists have hypothesized that the gamma rays might be shock waves from stars being consumed by the massive black hole at the center of the galaxy.

2. Rectangular Galaxy

“Look, up in the sky! It’s a…rectangle?” Earlier this year, astronomers spotted a celestial body, roughly 70 million light-years away, with an appearance that is unique in the visible universe: The galaxy LEDA 074886 is shaped more or less like a rectangle. While most galaxies are shaped like discs, three-dimensional ellipses or irregular blobs, this one seems to have a regular rectangle or diamond-shaped appearance. Some have speculated that the shape results from the collision of two spiral-shaped galaxies, but no one knows for now.

3. The Moon’s Magnetic Field

One of the moon’s greatest mysteries—why only some parts of the crust seem to have a magnetic field—has intrigued astronomers for decades, even inspiring the buried mythical “monolith” in the novel and film 2001: A Space Odyssey. But some scientists finally think they may have an explanation. After using a computer model to analyze the moon’s crust, researchers believe the magnetism may be a relic of a 120-mile-wide asteroid that collided with the moon’s southern pole about 4.5 billion years ago, scattering magnetic material. Others, though, believe the magnetic field may be related to other smaller, more recent impacts.

4. Why Do Pulsars Pulse?

Pulsars are distant, rapidly spinning neutron stars that emit a beam of electromagnetic radiation at regular intervals, like a rotating lighthouse beam sweeping over a shoreline. Although the first one was discovered in 1967, scientists have for decades struggled to understand what causes these stars to pulse—and, for that matter, what causes pulsars to occasionally stop pulsing. In 2008, though, when one pulsar suddenly shut off for 580 days, scientists’ observations allowed them to determine that the “on” and “off” periods are somehow related to magnetic currents slowing down the stars’ spin. Astronomers are still at work trying to understand why these magnetic currents fluctuate in the first place.

5. What Is Dark Matter?

Astrophysicists are currently trying to observe the effects of dark energy [link to Fast Forward], which accounts for some 70 percent of the universe. But it’s not the only dark stuff in the cosmos: roughly 25 percent of it is made up of an entirely separate material called dark matter. Completely invisible to telescopes and the human eye, it neither emits nor absorbs visible light (or any form of electromagnetic radiation), but its gravitational effect is evident in the motions of galaxy clusters and individual stars. Although dark matter has proven extremely difficult to study, many scientists speculate that it might be composed of subatomic particles that are fundamentally different from those that create the matter we see around us.

6. Galactic Recycling

In recent years, astronomers have noticed that galaxies form new stars at a rate that would seem to consume more matter than they actually have inside them. The Milky Way, for example, appears to turn about one sun’s worth of dust and gas into new stars every year, but it doesn’t have enough spare matter to keep this up long-term. A new study of distant galaxies might provide the answer: Astronomers noticed gas that had been expelled by the galaxies flowing back in to the center. If the galaxies recycle this gas to produce new stars, it might be a piece of the puzzle in solving the question of the missing raw matter.

7. Where Is All the Lithium?

Models of the Big Bang indicate that the element lithium should be abundant throughout the universe. The mystery, in this case, is pretty straightforward: it doesn’t. Observations of ancient stars, formed from material most similar to that produced by the Big Bang, reveal amounts of lithium two to three times lower than predicted by the theoretical models. New research indicates that some of this lithium may be mixed into the center of stars, out of view of our telescopes, while theorists suggest that axions, hypothetical subatomic particles, may have absorbed protons and reduced the amount of lithium created in the period just after the Big Bang.

8. Is There Anybody Out There?

In 1961, astrophysicist Frank Drake devised a highly controversial equation: By multiplying together a series of terms relating to the probability of extraterrestrial life (the rate of star formation in the universe, the fraction of stars with planets, the fraction of planets with conditions suitable for life, etc.) he surmised that the existence of intelligent life on other planets is extremely likely. One problem: Roswell conspiracy theorists notwithstanding, we haven’t heard from any aliens to date. Recent discoveries of distant planets that could theoretically harbor life, though, have raised hopes that we might detect extraterrestrials if we just keep looking.

9. How Will the Universe End? [Warning, Potential Spoiler Alert!]

We now believe the universe started with the Big Bang. But how will it end? Based on a number of factors, theorists conclude that the fate of the universe could take one of several wildly different forms. If the amount of dark energy is not enough to resist the compressing force of gravity, the entire universe could collapse into a singular point—a mirror image of the Big Bang, known as the Big Crunch. Recent findings, though, indicate a Big Crunch is less likely than a Big Chill, in which dark energy forces the universe into a slow, gradual expansion and all that remains are burned-out stars and dead planets, hovering at temperatures barely above absolute zero. If enough dark energy is present to overwhelm all other forces, a Big Rip scenario could occur, in which all galaxies, stars and even atoms are torn apart.

10. Across the Multiverse

Theoretical physicists speculate that our universe may not be the only one of its kind. The idea is that our universe exists within a bubble, and multiple alternative universes are contained within their own distinct bubbles. In these other universes, the physical constants—and even the laws of physics—may differ drastically. Despite the theory’s resemblance to science fiction, astronomers are now looking for physical evidence: Disc-shaped patterns in the cosmic background radiation left over from the Big Bang, which could indicate collisions with other universes.

ikenbot:

M8 and M20 in Narrow Band

by César Cantú