Category Archives: Milky Way

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Rattling the Galaxy’s Bones

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Dark Cloud in the Milky Way

The galactic “bone” was identified while studying a dust cloud that in 2010 was nicknamed “Nessie” after the Loch Ness Monster. Nessie turns out to be at least twice, and perhaps as much as eight times, longer than originally claimed. Both the original 2010 “Nessie” and the extended structure are outlined and labeled here on a Spitzer infrared image.
Credit: NASA/JPL/SSC

Once in a while a story really grabs my attention, like yesterday’s census of planets in the Milky Way.  It really opened up a galaxy of possible worlds to explore. Today, I was sitting in a press conference, listening to astronomers talking about using radio astronomy to study a cloud of gas and dust that they described as the one of the Milky Way’s “bones”, meaning an important part of its structure.

The structure is nicknamed “Nessie” because it bears a resemblance to the Loch Ness Monster. That right there was enough to grab my attention because as CEO of Loch Ness Productions, I’m quite used to being called one of the “Nessies” by our colleagues in the field. So, I approve of my monstrous namesake in the sky!

It’s a cool name and a memorable mental visual.

So, what’s Nessie all about?

Think about our galaxy. It’s what’s known as a barred spiral galaxy. That means it is a typical spiral — with two principal spiral arms wrapping around, and a bar cutting across the middle.

The central region of our the Milky Way has tantalized astronomers since forever, but it’s tough to see because it’s hidden by clouds of gas and dust. However, if you look at it in infrared light or using radio telescopes, you can make out structures not only in the core but along the plane of the Milky Way.

Astronomers have done that using a variety of techniques. In the case of Nessie, they used the Spitzer Space Telescope to probe along the plane (a line drawn across the central region from edge to edge) and found this cloud feature that got nicknamed Nessie by James Jackson of Boston University.

Alyssa Goodman at Harvard Center for Astrophysics and her team looked at Nessie and analyzed it using various data set. It’s really a long tendril of dust and gas that they called a “bone.”

Goodman gave a talk at the AAS today about Nessie. “This is the first time we’ve seen such a delicate piece of the galactic skeleton,” she said, and pointed out that other spiral galaxies also display internal bones or endoskeletons. Observations, especially at infrared wavelengths of light, have found long skinny features jutting between galaxies’ spiral arms. These relatively straight structures are much less massive than the curving spiral arms.

Computer simulations of galaxy formation show webs of filaments within spiral disks. It is very likely that the newly discovered Milky Way feature is one of these “bone-like” filaments.

Radio emissions from clouds of molecular gas in the center of the Milky Way region show that Nessie is in the galactic plane, and is more than 300 light-years long but only 1 or 2 light-years wide. The amount of mass is enough to make about  100,000 Suns. It’s possible that this odd feature bone is part of a spiral arm, or maybe is part of a web connecting other spiral features. Goodman and her colleagues hope to find more of these bones, and once they have enough data, it will give them enough information to create a cool 3D version of the galaxy and its skeleton.

 

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Getting the Stellar Boot

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Hyper-Velocity Star Wanders in the Wrong Neighborhood

An artist's conception of a star getting the boot from the Milky Way Galaxy. Courtesy: STScI

What happens when a little group of stars traveling together through the galaxy find themselves in the wrong neighborhood? If it’s the hyper-velocity (meaning super-fast, moving at 2.5 million kilometers per hour, or three times the Sun’s velocity through space) hot blue, supermassive star  HE 0437-5439, then the scenario is one worthy of a TV detective show.

It’s one that astronomers have pieced together, like CSI technicians at a cosmic crime scene.  The only evidence they have is the star itself.   It’s hot, massive, and blue.  It’s at least 100 million years old, since that’s how long it would take for such a fast-moving object to travel out along the trajectory it has been following from the center of the Milky Way. By all rights, a 100-million-year-old star this massive should have burned out by now. Instead, there it is, speeding away from something that happened to it.

The most likely explanation for the star’s blue color and extreme speed is that it was part of a triple-star system traveling happily along through the galaxy. At some point it wandered in the wrong place. That started a gravitational billiard-ball game with the galaxy’s monster black hole. And, where three stars were first involved, one got sucked into the black hole and the other two merged to create the hot, massive star that then got the gravitational kick out of the galaxy.

This concept for imparting an escape velocity on stars was first proposed in 1988. The theory suggests that the Milky Way’s black hole should eject a star about once every 100,000 years. And so, here is HE 0437-5439, a supermassive blue star that should be dead by now, but instead it’s blasting away from the Milky Way, having once been the leftover pair of stars given the boot by a gravitational assist from the unlucky third member of the triplet as it was devoured by the black hole.

As the remaining pair rocketed away, they went on with normal stellar evolution. One of the pair wa a massive star and it puffed up to become a red giant. Eventually, it enveloped its partner. The two spiraled together and eventually merged into the superstar “blue straggler” we see today.

So, as they say on one of the CSI episodes on TV: what’s the evidence? How can we know what happened hundred million years ago and to such a massive star?  Based on the speed and position of HE 0437-5439, the star would have to be at least 100 million years old to have journeyed from the Milky Way’s core. Yet its mass — nine times that of our Sun — and blue color mean that it should have burned out after only 20 million years — far shorter than the transit time it took to get to its current location.

To solve the puzzle of a massive star traveling so fast away from the core of the galaxy required a number of observations to chart the star’s path. It was first discovered by the Hamburg/European Southern Observatory survey in 2005.   HE 0437-5439 was then observed by the Hubble Space Telescope, which charted the star’s position in 2009. Astronomers then compared that position with positions calculated in the images taken in 2006. They could figure out its trajectory, which took it very near the core of our galaxy. The rest of the story is based on deducing the mass of the star and then using stellar evolution to come up with a plausible scenario of how such a massive star could end up where it is, traveling so fast.

There are more of these high-speed stragglers to study, and astronomers may likely find that some of them also wandered where they shouldn’t have, suffering a similar fate to the progenitors of HE 0437-5439. Stay tuned!