Author: Fraser Cain

When stars like our Sun run out of fuel, they flare briefly as a red giant, and then settle down as a white dwarf. No longer fusing elements together, they slowly cool down over billions of years, radiating their heat away into the Universe. But just as they enter this final stage of life, white dwarf stars might get a powerful kick, pushing them through space, and out of the stellar clusters where they’ve spent their entire lives.

This discovery was made by a team of astronomers from the University of British Columbia. They were performing a detailed survey of the globular cluster NGC 6397; one of the closest clusters in the Milky Way.

They were categorizing the stars by mass, and then determining their position in the cluster. They expected that high mass stars should sink down to the middle, and the low mass stars should be flung out to the outer reaches of the cluster. And this is exactly what they saw for the stars.

But for some reason, the white dwarf stars were pushed to the outskirts of the cluster. Even though they had started out as regular stars, when they made the transition to white dwarf, they were hurried out of the cluster.

So what process could give these white dwarfs the boot?

Using computer simulations, UBC astronomers Harvey Richer and his colleagues calculated that when a white dwarf is born, they eject large quantities of mass. If this mass is ejected in only one direction in space, it acts like a natural rocket engine.

“Newly-minted white dwarfs should be near the center, but they are not,” says Richer. “Our idea is that when these white dwarfs were born, they were given a small kick of 7,000 to 11,000 miles an hour (three to five kilometers a second), which rocketed them to the outer reaches of the cluster.”

Original Source: UBC News Release

The most common kinds of star in the Universe are M-dwarf stars. They’re normally cool (a mere 2,400 Kelvin), small (typically 8-10% the mass of the Sun) and quiet – really pretty boring for stars. But astronomers have found one that’s going against the grain. It has a strong magnetic field; greater even than our own Sun’s. And it has a huge hot spot that spans half of its surface.

Although the science about the star, TVLM513-46546, is pretty interesting, just think about the fact that researchers were actually able to detect it at all. Astronomers are able to measure a tiny star’s magnetic field, and locate a hot spot on its surface from 35 light-years away. Amazing stuff.

Okay, onto the discovery. It was made by combining data from several different observatories in different wavelengths: radio data from the Very Large Array, spectra from the Gemini North 8-metre telescope, ultraviolet from Swift, and X-rays from Chandra.

Over the course of their observations, the researchers learned that the star has steady radio emissions, but these are punctuated by minute-long firework displays coming from collisions of magnetic fields in the corona of the star. As the magnetic field lines connect and reconnect, enormous amounts of energy are released. These releases match soft X-ray emissions and X-ray flares.

Perhaps the most interesting is this enormous hot spot. The researchers were able to measure that half of the star is much brighter, and turns every two days with the rotation of the star. This is a total mystery to the researchers. “We still do not know why only half of the star is lit up in hydrogen and if this situation remains unchanged over days, weeks, years, or centuries,” remarked Edo Berger, a Carnegie-Princeton postdoctoral fellow.

The magnetic activity could mean that there’s unusual activity beneath the star’s surface. Or maybe there’s an undiscovered companion object interacting with the star. Nothing’s been seen so far, but it could be there.

The researchers are planning to study other examples of these ultracool M-dwarf stars and see if this is a common for many of them, or this star is just an anomaly.

Original Source: Gemini News Release

Didn’t I just mention how the press agencies try to relate an image to the holidays? This time, ESA has release an image they think looks like Santa Claus. I don’t see it. Maybe the massive star forming region blazing in X-rays is his beard. Or the dusty surrounding clouds is the reindeer. Nope, I still don’t see it.

The science, though, is very cool.

The image, captured by ESA’s XMM-Newton X-ray observatory is of the Orion Nebula; one of the most famous places in space. The bright star that dominates the image is theta1 Orionis C, a giant star with 40 times the mass of the Sun.

Astronomers think that the collision between the wind from the star and the surrounding gas has heated the environment up to millions of degrees. Hot gas like this has been seen around the most vigorous star forming regions in galaxies, but never around such a small collection of stars.

In optical and infrared images of the region, the highest temperature regions of the nebula just look like a big cavity. But under the view of XMM-Newton, what looks like empty space is actually glowing in X-rays.

A team working with the observatory discovered this cloud of gas while they were doing a survey of the young stars in the region. There was a faint background glow of X-rays in many of the stars. After this was seen several times, the astronomers decided to see if it was actually in the background everywhere.

Researcher Manuel Güdel proposes that this could be an additional way for heavy elements to get into space. “This is another possible way to enrich the interstellar medium. You don’t have to wait for a sudden supernova to explode. You can do it with just one or two massive stars over millions of years.”

Oh wait, that top part is Santa’s hat, and that bottom part is his beard? I’ll keep trying to see it.

Original Source: ESA News Release

It’s always exciting to see an idea in theory verified with real observations. For the first time, astronomers have observed a theoretical stage in stellar evolution, when a star’s envelope is beginning to flatten and collapse, and streams of gas are escaping out. New observations by NASA’s Spitzer Space Telescope have spotted a young star right at this stage, blasting out material in powerful jets.

The new research will be published in the December 1st edition of Astrophysical Journal Letters. It provides observational evidence to this specific stage in the currently accepted model of stellar evolution.

Researchers from several universities observed a newly forming star called L1157, located about 800 light-years away in the constellation Cepheus. The star is only 10,000 years old, and still has a million years or so to go before it ignites as a star like our Sun.

New stars are born out of vast clouds of cold gas and dust. As the collective gravity of the gas pulls inward, the whole collection starts to spin. As the star grows in the middle, it spins faster and faster, and a disk of planet-forming material forms around it. Powerful jets fire off from the top and bottom of the star to relieve its accumulating pressure. Eventually the envelope of material falls onto the spinning disk, and the jets halt.

Here’s the problem in watching this process: dust. Newborn stars are surrounded in a halo of dust that visible light telescopes can’t penetrate. Fortunately, the infrared view of telescopes like Spitzer can see right through the dust, to learn what’s going on inside.

The twin jets blasting off of L1157 are huge; each one is .75 light years long. The hottest parts of the jet (seen in white in the image) are about 100 degrees Celsius (212 degrees F), but the remainder is down around zero.

The planetary disk itself is the dark band in the middle of the image, dark and hazy. In fact, it’s clogged with so much dust that not even Spitzer can see through it.

Original Source: NASA/JPL/Spitzer News Release