milky way Archives

February 15, 2013December 23, 2015 by Jason Major

Galactic Gas Cloud Could Help Spot Hidden Black Holes

Illustration of gas cloud G2 approaching Sgr A* . Our central supermassive black hole periodically snacks on clouds and other material like this. That gives off X-rays and other emissions. (ESO/MPE/M.Schartmann/J.Major)

The heart of our Milky Way galaxy is an exotic place. It’s swarming with gigantic stars, showered by lethal blasts of high-energy radiation and a veritable cul-de-sac for the most enigmatic stellar corpses known to science: black holes. And at the center of the whole mélange is the granddaddy of all the black holes in the galaxy — Sagittarius A*, a supermassive monster with 4 million times more mass than the Sun packed into an area smaller than the orbit of Mercury.

Sgr A* dominates the core of the Milky Way with its powerful gravity, trapping giant stars into breakneck orbits and actively feeding on anything that comes close enough. Recently astronomers have been watching the movement of a large cloud of gas that’s caught in the pull of Sgr A* — they’re eager to see what exactly will happen once the cloud (designated G2) enters the black hole’s dining room… it will, in essence, be the first time anyone watches a black hole eat.

But before the dinner bell rings — estimated to be sometime this September — the cloud still has to cover a lot of space. Some scientists are now suggesting that G2’s trip through the crowded galactic nucleus could highlight the locations of other smaller black holes in the area, revealing their hiding places as it passes.

In a new paper titled “G2 can Illuminate the Black Hole Population near the Galactic Center” researchers from Columbia University in New York City and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts propose that G2, a cloud of cool ionized gas over three times more massive than Earth, will likely encounter both neutron stars and other black holes on its way around (and/or into) SMBH Sgr A*.

*Estimated number of stellar-mass black holes to be encountered by G2 along its trajectory (Bartos et al.)*

The team notes that there are estimated to be around 20,000 stellar-mass black holes and about as many neutron stars in the central parsec of the galaxy. (A parsec is equal to 3.26 light-years, or 30.9 trillion km. In astronomical scale it’s just over 3/4 the way to the nearest star from the Sun.) In addition there may also be an unknown number of intermediate-mass black holes lurking within the same area.

These ultra-dense stellar remains are drawn to the center region of the galaxy due to the effects of dynamical friction — drag, if you will — as they move through the interstellar material.

Of course, unless black holes are feeding and actively throwing out excess gobs of hot energy and matter due to their sloppy eating habits, they are very nearly impossible to find. But as G2 is observed moving along its elliptical path toward Sgr A*, it could very well encounter a small number of stellar- and intermediate-mass black holes and neutron stars. According to the research team, such interactions may be visible with X-ray spotting spacecraft like NASA’s Chandra and NuSTAR.

*NuSTAR X-ray image of a flare emitted by Sgr A* in July 2012 (NASA/JPL-Caltech)*

The chances of G2 encountering black holes and interacting with them in such a way as to produce bright enough x-ray flares that can be detected depends upon a lot of variables, like the angles of interaction, the relative velocities of the gas cloud and black holes, the resulting accretion rates of in-falling cloud matter, and the temperature of the accretion material. In addition, any observations must be made at the right time and for long enough a duration to capture an interaction (or possibly multiple interactions simultaneously) yet also be able to discern them from any background X-ray sources.

Still, according to the researchers such observations would be important as they could provide valuable information on galactic evolution, and shed further insight into the behavior of black holes.

Read the full report here, and watch an ESO news video about the anticipated behavior of the G2 gas cloud around the SMBH Sgr A* below:

This research was conducted by Imre Bartos, Zoltán Haiman, and Bence Kocsis of Columbia University and Szabolcs Márka of the Harvard-Smithsonian Center for Astrophysics.

February 10, 2013December 23, 2015 by Jason Major

A Cosmic Snake for Chinese New Year

Barnard 72 - the "Snake Nebula" (Wikisky.org)

Gong Hey Fat Choy! Today marks the beginning of the Chinese New Year and what better way to celebrate the Year of the Black Snake than with a look at an enormous shadowy cosmic serpent, the Snake Nebula!

Also known as Barnard 72, the Snake Nebula is a meandering lane of dark dust located about 650 light-years away in the constellation Ophiuchus. Several light-years long, its opaque dust blocks our view of stars within the central bulge of the galaxy… but also reveals its presence since that region of the sky is literally filled with stars.

The Snake Nebula is part of the larger Dark Horse Nebula.

The bright star seen in the image just below the snake’s middle (looks like it may have just had dinner!) is HD 157398, a giant orange star 538 light-years from Earth. Here it shines brightly, but in the sky its visible magnitude is 6.67 — just a bit dimmer than what can be seen with the naked eye under the darkest skies.

Image via Wikisky.org.

January 25, 2013June 5, 2022 by Ken Kremer

NASA: Reaches for New Heights – Greatest Hits Video

Video Caption: At NASA, we’ve been a little busy: landing on Mars, developing new human spacecraft, going to the space station, working with commercial partners, observing the Earth and the Sun, exploring our solar system and understanding our universe. And that’s not even everything.Credit: NASA

Check out this cool action packed video titled “NASA: Reaching for New Heights” – to see NASA’s ‘Greatest Hits’ from the past year

The 4 minute film is a compilation of NASA’s gamut of Robotic Science and Human Spaceflight achievements to explore and understand Planet Earth here at home and the heavens above- ranging from our Solar System and beyond to the Galaxy and the vast expanse of the Universe.

Image caption: Planets and Moons in perspective. Credit: NASA

The missions and programs featured include inspiringly beautiful imagery from : Curiosity, Landsat, Aquarius, GRACE, NuSTAR, GRAIL, Dawn at Asteroid Vesta, SDO, X-48C Amelia, Orion, SLS, Apollo, SpaceX, Sierra Nevada Dream Chaser, Boeing CST-100, Commercial Crew, Hurricane Sandy from the ISS, Robonaut and more !

And even more space exploration thrills are coming in 2013 !

Ken Kremer

Image caption: SpaceX Falcon 9 rocket blasts off on May 22, 2012 with Dragon cargo capsule from Space Launch Complex-40 at Cape Canaveral Air Force Station, Fla., on the first commercial mission to the International Space Station. The next launch is set for March 1, 2013. Credit: Ken Kremer

January 9, 2013December 23, 2015 by Nancy Atkinson

Astronomers Find a “Spine” Along Spiral Arms of the Milky Way

Researchers have identified the first "bone" of the Milky Way - a long tendril of dust and gas that appears dark in this infrared image from the Spitzer Space Telescope. Running horizontally along this image, the "bone" is more than 300 light-years long but only 1 or 2 light-years wide. It contains about 100,000 suns' worth of material. Credit: NASA/JPL/SSC

Astronomers have found what may be considered a piece of a galactic skeleton; a dark structure of gas and dust that might provide a backbone on which one of the spiral arms extend from the central bar of the Milky Way galaxy.

“This ‘bone’ is likely made from high density gas — the type that forms stars — and while the feature that we see is a sinuous distinction you get from dust, there is a huge amount of gas,” said Alyssa Goodman of the Harvard-Smithsonian Center for Astrophysics (CfA) at a press conference at the American Astronomical Society meeting in Long Beach, California today. “But we just don’t know yet what it is.”

A flipped image of IC342, in which a 'backbone' structure can be seen in the spiral arms. Credit: Jarret et al. 2012; WISE Enhanced Resolution Galaxy Atlas.

While this is the first time such a structure has been seen in our own galaxy, other spiral galaxies seemingly display internal “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.

Goodman said that since we view the Milky Way from the inside, its exact structure is difficult to determine, but it is thought to have a central bar and two major spiral arms that wrap around its disk.

A team of astronomers first spotted the galactic bone while studying a dust cloud nicknamed “Nessie,” since its shape is reminiscent of the Loch Ness monster. The central part of the “Nessie” bone was discovered in Spitzer Space Telescope data in 2010 by James Jackson (Boston University). With further analysis, Goodman’s team determined the dark cloud goes way beyond the original section that was first found, and is as much as eight times longer than Jackson’s original sighting.

Radio emissions from molecular gas show that the feature is not a chance projection of material on the sky, but instead a real feature. Not only is “Nessie” in the galactic plane, but also it extends much longer than anyone anticipated. This slender bone of the Milky Way is more than 300 light-years long but only 1 or 2 light-years wide. It contains about 100,000 suns’ worth of material, and now looks more like a cosmic snake.

“This bone is much more like a fibula – the long skinny bone in your leg – than it is like the tibia, or big thick leg bone,” Goodman said.

It lies along the plane of the Milky Way, and since our vantage point is just above the the plane, Goodman and her team are hopeful that the skeleton may be able to be mapped.

“It’s possible that the ‘Nessie’ bone lies within a spiral arm, or that it is part of a web connecting bolder spiral features. Our hope is that we and other astronomers will find more of these features, and use them to map the skeleton of the Milky Way in 3-D,” she said.

The team’s paper is not quite finished yet, but it is online on the new open source scientific collaboration site, Authorea.

For more information, visit http://milkywaybones.org.

Source: CfA, AAS

December 4, 2012December 23, 2015 by Jason Major

Black Hole Jets Might Be Molded by Magnetism

Visible-light Hubble image of the jet emitted by the 3-billion-solar-mass black hole at the heart of galaxy M87 (Feb. 1998) Credit: NASA/ESA and John Biretta (STScI/JHU)

Even though black holes — by their definition and very nature — are the ultimate hoarders of the Universe, gathering and gobbling up matter and energy to the extent that not even light can escape their gravitational grip, they also often exhibit the odd behavior of flinging vast amounts of material away from them as well, in the form of jets that erupt hundreds of thousands — if not millions — of light-years out into space. These jets contain superheated plasma that didn’t make it past the black hole’s event horizon, but rather got “spun up” by its powerful gravity and intense rotation and ended up getting shot outwards as if from an enormous cosmic cannon.

The exact mechanisms of how this all works aren’t precisely known as black holes are notoriously tricky to observe, and one of the more perplexing aspects of the jetting behavior is why they always seem to be aligned with the rotational axis of the actively feeding black hole, as well as perpendicular to the accompanying accretion disk. Now, new research using advanced 3D computer models is supporting the idea that it’s the black holes’ ramped-up rotation rate combined with plasma’s magnetism that’s responsible for shaping the jets.

In a recent paper published in the journal Science, assistant professor at the University of Maryland Jonathan McKinney, Kavli Institute director Roger Blandford and Princeton University’s Alexander Tchekhovskoy report their findings made using computer simulations of the complex physics found in the vicinity of a feeding supermassive black hole. These GRMHD — which stands for General Relativistic Magnetohydrodynamic — computer sims follow the interactions of literally millions of particles under the influence of general relativity and the physics of relativistic magnetized plasmas… basically, the really super-hot stuff that’s found within a black hole’s accretion disk.

What McKinney et al. found in their simulations was that no matter how they initially oriented the black hole’s jets, they always eventually ended up aligned with the rotational axis of the black hole itself — exactly what’s been found in real-world observations. The team found that this is caused by the magnetic field lines generated by the plasma getting twisted by the intense rotation of the black hole, thus gathering the plasma into narrow, focused jets aiming away from its spin axes — often at both poles.

At farther distances the influence of the black hole’s spin weakens and thus the jets may then begin to break apart or deviate from their initial paths — again, what has been seen in many observations.

This “magneto-spin alignment” mechanism, as the team calls it, appears to be most prevalent with active supermassive black holes whose accretion disk is more thick than thin — the result of having either a very high or very low rate of in-falling matter. This is the case with the giant elliptical galaxy M87, seen above, which exhibits a brilliant jet created by a 3-billion-solar-mass black hole at its center, as well as the much less massive 4-million-solar-mass SMBH at the center of our own galaxy, Sgr A*.

Using these findings, future predictions can be better made concerning the behavior of accelerated matter falling into the heart of our galaxy.

Read more on the Kavli Institute’s news release here.

Inset image: Snapshot of a simulated black hole system. (McKinney et al.) Source: The Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)

November 26, 2012December 23, 2015 by Nancy Atkinson

Astrophoto: Beam Me Up!

Light beams and the Milky Way. Credit: Peter Greig (St1nkyPete on Flickr)

This great shot of the Milky Way includes some mysterious beams of light. But astrophotographer Peter Greig supplies the festive explanation: “This is a shot I took in Soisdorf, Germany earlier this year,” he writes. “The beams of light on the right are coming from a carnival in a nearby village!”

This photo was taken on September 7, 2012 using a Canon EOS 550D.

Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

November 19, 2012January 4, 2016 by Nancy Atkinson

Stunning New Timelapse: Storms and Stars at Joshua Tree

Here’s another gorgeous timelapse by Gavin Heffernan, who returned to Joshua Tree National Park in California for his third look at the incredible night sky. “It was an epic night,” Gavin told UT, “with storms at first, then some of the clearest skies I’ve ever seen.”

The sky is ablaze with activity; the rolling storm, the Milky Way in all its glory, plus meteors, satellites and aircraft passing overhead. Gavin and his Sunchaser Pictures team shot the footage with a Canon 7D and Canon 5D, with a 24mm/1.4 lens and a 28mm/1.8. Most intervals are 25 seconds, except the 1st, which is 30 second, Gavin said.

If you like this one, take a look at Gavin’s first and second visits to Joshua Tree, too.

JOSHUA TREE JOURNEY 3: STORM from Sunchaser Pictures on Vimeo.

November 14, 2012December 23, 2015 by Nancy Atkinson

Explore the Stellar Neighborhood with New Milky Way Visualization

Screenshot from 100,000 Stars

Want to explore the Milky Way? A new visualization tool from Google called 100,000 Stars lets you take a tour of our cosmic neighborhood, and with a few clicks of your mouse you can zoom in, out and around and do a little learning along the way. Zoom in to learn the names of some of the closest stars; click on the names to find out more information about them.

Playing with it is great fun, and I’ve been experimenting with it for a while. The most important caveat about 100,000 Stars is that you need to run it in Chrome. It’s from the Chrome Experiment team, and it uses imagery and data from NASA and ESA, but the majority of what you are seeing are artist’s renditions.

The best way to get started is to click on the Take the Tour in the upper left hand corner.

But if you just want to zoom in, you can see the closest stars to us. The Sun is in the middle, and if you zoom in even further, you’ll see the Oort Cloud. Keep zooming in to find the planetary orbits (I was struck by how much zooming had to be done to get to the planets, giving a sense of scale).

It includes some nifty spacey-like music (provided by Sam Hulick, who video game fans may recognize as a composer for the popular space adventure series, Mass Effect) but if you’d rather explore in silence, hit your mute button.

What I enjoyed the most is moving my mouse up and down to see the 3-D effect of how everything fits together, providing a sense of the cosmic web that holds our universe together.

Check out 100,000 Stars

November 7, 2012April 26, 2016 by Nancy Atkinson

The Milky Way’s Black Hole Shoots Out Brightest Flare Ever

This false-color image shows the central region of our Milky Way Galaxy as seen by Chandra. The bright, point-like source at the center of the image was produced by a huge X-ray flare that occurred in the vicinity of the supermassive black hole at the center of our galaxy.
Image: NASA/MIT/F. Baganoff et al.

For some unknown reason, the black hole at the center of the Milky Way galaxy shoots out an X-ray flare about once a day. These flares last a few hours with the brightness ranging from a few times to nearly one hundred times that of the black hole’s regular output. But back in February 2012, astronomers using the Chandra X-Ray Observatory detected the brightest flare ever observed from the central black hole, also known as Sagittarius A*. The flare, recorded 26,000 light years away, was 150 times brighter than the black hole’s normal luminosity.

What causes these outbursts? Scientists aren’t sure. But Sagittarius A* doesn’t seem to be slowing down, even though as black holes age they should show a decrease in activity.

The supermassive black hole at the center of the Milky Way galaxy. — Mysterious X-ray flares caught by Chandra may be asteroids falling into the Milky Way's giant black hole. Credit: X-ray: NASA/CXC/MIT/F. Baganoff et al.; Illustrations: NASA/CXC/M.Weiss

Earlier this year, a group of researchers said that the outbursts may come from asteroids or even wandering planets that come too close to the black hole and they get consumed. Basically, the black hole is eating asteroids and then belching out X-ray gas.

Astronomers involved in this new observation seem to concur with that line of thinking.

“Suddenly, for whatever reason, Sagittarius A* is eating a lot more,” said Michael Nowak, a research scientist at MIT Kavli and co-author of a new paper in the Astrophysical Journal. “One theory is that every so often, an asteroid gets close to the black hole, the black hole stretches and rips it to pieces, and eats the material and turns it into radiation, so you see these big flares.”

Astronomers detect black holes by the light energy given off as they swallow nearby matter. The centers of newborn galaxies and quasars can appear extremely bright, giving off massive amounts of energy as they devour their surroundings. As black holes age, they tend to slow down, consuming less and appearing fainter in the sky.

“Everyone has this picture of black holes as vacuum sweepers, that they suck up absolutely everything,” says Frederick K. Baganoff, another co-author from MIT. “But in this really low-accretion-rate state, they’re really finicky eaters, and for some reason they actually blow away most of the energy.”

While such events like this big blast appear to be relatively rare, Nowak suspects that flare-ups may occur more frequently than scientists expect. The team has reserved more than a month of time on the Chandra Observatory to study Sagittarius A* in hopes of identifying more flares, and possibly what’s causing them.

“These bright flares give information on the flaring process that isn’t available with the weaker ones, such as how they fluctuate in time during the flare, how the spectrum changes, and how fast they rise and fall,” said Mark Morris from UCLA. “The greatest importance of this bright flare may be that it builds up the statistics on the characteristics of strong flares that can eventually be used to [identify] the cause of such flares.”

Even more intriguing to Baganoff is why the black hole emits so little energy. In 2003, he ran the very first observations with the then-new Chandra Observatory, and calculated that, given the amount of gas in its surroundings, Sagittarius A* should be about a million times brighter than it is — a finding that suggested the black hole throws away most of the matter it would otherwise consume.

The physics underlying such a phenomenon remain a puzzle that Baganoff and others hope to tease out with future observations.

“We’re really studying the great escape, because most of the gas escapes, and that’s not what we expect,” Baganoff says. “So we’re piecing out the history of the activity of the center of our galaxy.”

Paper: Chandra/HETGS Observations of the Brightest Flare seen from Sgr A*

See a movie of the flare here.

Source: MIT

October 29, 2012December 23, 2015 by Nancy Atkinson

Astronomers Uncover a Crime of Galactic Proportions

As the Milky Way rises over the horizon at the European Southern Observatory, its companion galaxies also come into view. Credit: ESO/Y. Beletsky

A previously undetected heist of stars was uncovered by astronomers who were actually looking for why an unexpected amount of microlensing events were being seen around the outskirts of the Milky Way. Instead, they found the Large Magellanic Cloud (LMC) had been stealing stars from its neighbor, the Small Magellanic Cloud (SMC), leaving behind a trail of stars. Although the crime was likely committed hundreds of milllions of years ago during a collision between the two galaxies, the new information is helping astronomers to understand the history of these two galaxies that are in our neighborhood.

“You could say we discovered a crime of galactic proportions,” said Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.

The Large Magellanic Cloud almost got away with it, if it wasn’t for those meddling astronomers….

Astronomers were originally monitoring the LMC to hunt for the reason for the unexpected microlensing events. Their initial hypothesis was that massive compact halo objects, or MACHOs were causing the effect, where a nearby object passes in front of a more distant star. The gravity of the closer object bends light from the star like a lens, magnifying it and causing it to brighten. The MACHOs were thought to be faint objects, roughly the mass of a star, but not much is known about them. Several surveys looked for MACHOs in order to find out if they could be a major component of dark matter – the unseen stuff that holds galaxies together.

In order for MACHOs to make up dark matter, they must be so faint that they can’t be directly detected. So, the team of astronomers hoped to see MACHOs within the Milky Way by lensing distant LMC stars.

“We originally set out to understand the evolution of the interacting LMC and SMC galaxies,” said lead author of a new paper on the results, Gurtina Besla of Columbia University. “We were surprised that, in addition, we could rule out the idea that dark matter is contained in MACHOs.”

“Instead of MACHOs, a trail of stars removed from the SMC is responsible for the microlensing events,” said Loeb.

Only a fast-moving population of stars could yield the observed rate and durations of the microlensing events. The best way to get such a stellar population is a galactic collision, which appears to have occurred in the LMC-SMC system.

“By reconstructing the scene, we found that the LMC and SMC collided violently hundreds of millions of years ago. That’s when the LMC stripped out the lensed stars,” said Loeb.

Their research also supports recent findings suggesting that both Magellanic Clouds are on their first pass by the Milky Way.

However, this isn’t a closed case. The evidence for the trail of lensed stars is persuasive, but they haven’t been directly observed yet. A number of teams are searching for the signatures of these stars within a bridge of gas that connects the Magellanic Clouds.

The simulation results will be published in the Monthly Notices of the Royal Astronomical Society.

Read the team’s paper: The Origin of the Microlensing Events Observed Towards the LMC and the Stellar Counterpart of the Magellanic Stream

Source: CfA