Universe Today

When a star like our Sun dies, it’ll end up as a white dwarf. And if a star contains 1.4 times the mass of the Sun, it’ll have enough gravity to turn into a neutron star. Much bigger stars turn into black holes. But now it turns out, neutron stars can be much more massive than astronomers previously believed – and making black holes might be much more difficult.

Astronomers working with the Arecibo Observatory in Puerto Rico have increased the mass limit you need for a neutron star to turn into a black hole.

Paulo Freire, an astronomer from Arecibo presented his latest research at the Winter meeting of the American Astronomical Society, “the matter at the center of a neutron star is highly incompressible. Our new measurements of the mass of neutron stars will help nuclear physicists understand the properties of super-dense matter. It also means that to form a black hole, more mass is needed than previously thought. Thus, in our universe, black holes might be more rare and neutron stars slightly more abundant.

When these massive stars run out of fuel, they collapse down and then explode as a supernova. The core of the star is instantly compressed into a neutron star; an extreme object with a radius of roughly 10 to 16 km across and a density of billions of tonnes per cubic centimetre. A neutron star acts like a single, giant atomic nucleus.

Astronomers used to think that neutron stars needed between 1.6 and 2.5 times the mass of the Sun to collapse – any bigger and you’d get a neutron star. But the new evidence from Arecibo pushes this limit up to 2.7 times the mass of the Sun.

Although that sounds like a slight amount, it can actually have a significant impact on the ratio of neutron stars to black holes in the Universe.

In fact, scientists don’t fully understand how dense neutron stars can really be, and when they might actually switch over to become black holes, “the matter at the center of neutron stars is the densest in the Universe. It is one to two orders of magnitude denser than matter in the atomic nucleus. It is so dense we don’t know what it is made out of,” said Freire. “For that reason, we have at present no idea of how larger or how massive neutron stars can be.”

Original Source: Cornell University

As galaxies rotate, their spiral arms usually sweep back, trailing behind the rotation of the galaxy. But astronomers have found a galaxy that defies this convention, with its arms opening outward in the same direction as the rotation of the galaxy’s disk.

The galaxy, known as NGC 4622, lies 200 million light years away in the constellation Centaurus. A team of American astronomers analyzed images of the galaxy, and discovered that it has a previously hidden inner counter clockwise pair of spiral arms.

“Contrary to conventional wisdom, with both an inner counter-clockwise pair and an outer clockwise pair of spiral arms, NGC 4622 must have a pair of leading arms,” said Dr. Gene Byrd from the University of Alabama. “With two pairs of arms winding in opposite directions, one pair must lead and one pair must trail. Which way is which depends on the disk’s rotation. Alternatively, the inner counter clockwise pair must be the leading pair if the disk turns counter clockwise.”

This isn’t the first time the team announced their findings that NGC 4622 had a leading pair of spiral arms. Other astronomers were skeptical of the result, since the galaxy disk is only tilted 19 degrees from face-on, and clumpy clouds of dust could confuse the results.

The researchers came back and used two different independent techniques to verify the direction the arms are spinning.

Further observations are coming, since images from the Hubble Space Telescope revealed a dark dust lane in the centre of the galaxy. This suggests that NGC 4622 may have consumed a smaller companion galaxy, and this could help explain where the additional spiral arms came from.

Original Source: University of Alabama News Release

We live in a beautiful grand spiral galaxy. But how did we get from the primordial elements after the Big Bang to the intricate and complex structure we live in today? Astronomers have found some of the earliest galactic building blocks; the ancestors of galaxies like our own Milky Way.

The discovery was made by researchers from Rutgers and Penn State universities, and announced at the 211th meeting of the American Astronomical Society in Austin, Texas.

These newly discovered galaxies are tiny, between one-tenth and one-twentieth the mass of the Milky Way. From ground-based telescopes, they just look like individual stars. But the powerful gaze of the Hubble Space Telescope reveals them as regions of active star formation.

The researchers learned that these galaxies are hotbeds of star formation, blazing in a telltale spectrum of ultraviolet radiation that just screams, “I’ve got stellar nurseries”. In many cases, more than 10 of these proto-galaxies came together to form a single spiral galaxy.

“The Hubble Space Telescope delivered striking images of these early galaxies, with 10 times the resolution of ground-based telescopes,” said Caryl Gronwall, a senior research associate in Penn State’s Department of Astronomy & Astrophysics. “They come in a variety of shapes – round, oblong , and even somewhat linear – and we’re starting to make precise measurements of their sizes.”

The galaxies were discovered as part of a five-year census of galaxies in the early Universe. The astronomers searched for these specific kinds of galaxies by detecting the ultraviolet radiation from their bursts of star formation. They then performed follow up observations to find their distance and mass.

Original Source: Rutgers News Release

Astronomers think that many star systems actually contain multiple stars. There are doubles, triples and even quadruple groupings of stars locked together in a gravitational embrace. Astronomers recently discovered a system with 4 stars orbiting within the orbit of Jupiter. It’s a surprising discovery considering no telescope on Earth is powerful enough to separate them into distinct points of light.

The star system, located 166 light-years from here, is called BC 22 5866, and its discovery was announced the Winter meeting of the American Astronomical Society in Austin. An international team of astronomers described how they had been monitoring several hundred star systems when they saw something unusual.

They were analyzing the light from one of hundreds of stars when they realized that its light could be broken into 4 separate stars. Even the most powerful telescopes on Earth can’t actually resolve the stars into separate objects, and that means they’re close together… really close.

The stars are paired up together into binary groupings, and then these two pairs orbit a common centre of gravity. One pair orbits each other in less than 5 days – at a distance of a mere 0.06 astronomical units (1 AU is the distance from the Earth to the Sun). The second pair takes 55 days to complete an orbit, at a distance of 0.26 AU.

And finally, the two pairs take about 9 years to orbit one another at a distance of 5.8 AU – within the orbit of Jupiter in our own Solar System.

It must have been a very special system to allow 4 individual stars to form this closely together.

“The extraordinarily tight configuration of this stellar system tells us that there may have been a single gaseous disk that forced them into such small orbits within the first 100,000 years of their evolution, as the stars could not have formed so close to one another. This is the first evidence of a disk completely encompassing four stars,” says Dr. Shkolnik of the University of Hawaii’s Institute for Astronomy. “It is remarkable how much a single stellar spectrum can tell us about both the present and the past of these stars.”

Original Source: IfA News Release

An Einstein Ring happens when two galaxies are perfectly aligned. The closer galaxy acts as a lens, magnifying and distorting the view of a more distant galaxy. But today astronomers announced that they’ve discovered a double Einstein Ring: three galaxies are perfectly aligned, creating a double ring around the lensing galaxy. The odds of finding something like this are pretty low. And yet… here it is.

The double Einstein Ring image was captured by the Hubble Space Telescope, and shows a central galaxy surrounding by an almost complete ring, with another fainter ring around that. Think of a bull’s-eye.

It was found by an international team of astronomers led by Raphael Gavazzi and Tommaso Treu of the University of California, Santa Barbara, and the results were presented at the 211th meeting of the American Astronomical Society in Austin, Texas.

Treu was pretty excited, “the twin rings were clearly visible in the Hubble image. When I first saw it I said ‘wow, this is insane!’ I could not believe it!”

Here’s how it works. As Einstein predicted, gravity has the power to bend light. So instead of traveling on a straight curve, light that passes close to a large mass is pulled into a curved path. When you have a foreground galaxy perfectly lined up with a background galaxy, the light from the more distant galaxy is distorted into a ring of light.

Although the background galaxy is distorted, it’s also tremendously magnified, allowing astronomers to use the foreground galaxy as a natural telescope to peer much more deeply into the Universe than they would be able to see normally.

In the case of this double ring, the foreground galaxy is 3 billion light-years away. The background galaxy that forms the first ring is 6 billion light-years away, and the second background galaxy is 11 billion-light years away. This means that the background galaxy is being seen when the Universe was less than 3 billion years old.

The alignment also allowed astronomers to measure the mass of the middle galaxy to 1 billion solar masses. This is the first time the mass of a dwarf galaxy has been measured at this kind of distance.

Original Source: Hubble News Release