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Milky Way Galaxy
X-ray Astronomy Field Guide
Milky Way Galaxy
Questions and Answers
Milky Way Galaxy
Chandra Images
Milky Way Galaxy
Animations & Video: The Milky Way
Page 123
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1. Tour of SGR 1745-2900
QuicktimeMPEG In 2013, astronomers announced they had discovered a magnetar exceptionally close to the supermassive black hole at the center of the Milky Way using a suite of space-borne telescopes including NASA's Chandra X-ray Observatory.

Magnetars are dense, collapsed stars -- called "neutron stars" -- that possess enormously powerful magnetic fields. This magnetar, which astronomers named SGR 1745-2900, could be as close as two trillion miles from the black hole at the center of the Milky Way. While this may sound like a large distance, it is not in astronomical terms. In fact, this magnetar is by far the closest neutron star to a supermassive black hole ever discovered and is likely in its gravitational grip.

Since its discovery two years ago when it gave off a burst of X-rays, astronomers have been actively monitoring SGR 1745-2900 with Chandra and the European Space Agency's XMM-Newton. A new study uses these observations to reveal that the X-ray output from SGR 1745-2900 is dropping more slowly than for other magnetars, and its surface is hotter than expected.

What is causing this unusual behavior? The researchers propose the surface of the magnetar is being bombarded by charged particles. These particles may be trapped in twisted bundles of magnetic fields. This scenario could explain both the slow decline in X-rays as well as the hotter-than-usual surface temperature of SGR 1745-2900. Scientists will continue to study SGR 1745-2900 to glean more clues about what is happening with this magnetar as it orbits our Galaxy's giant black hole.
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(NASA/CXC/April Jubett)

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2. Megaflares Shed Light On Our Black Hole
QuicktimeMPEG Our Galaxy is shaped like a whirlpool, with long strips of cosmic gas and dust swirling around the center. And like a whirlpool, objects that float too close are dragged into the center never to be seen again.

The fate of these unfortunate objects is no mystery. Lurking in the dark at the heart of our Galaxy is gigantic, hungry monster - a supermassive black hole. Supermassive black holes are famous for their ability to swallow anything – even light! But they don't just eat; they sometimes spit too!

In late 2013, an outburst (what astronomers call 'flares') was spotted blasting from the center of our Galaxy. Like many flares, it was made up of high-energy X-rays. However, this particular outburst was 400 times brighter than the X-ray output normally seen coming from this black hole!

A little more than a year later, it let off another flare, this time it was 200 times brighter than usual.

Astronomers have two theories about what could be causing these so-called "megaflares". The first idea is that the black hole's strong gravity tore apart an asteroid that strayed too close. The debris was then heated to millions of degrees before being devoured.

The other possible explanation involves the strong magnetic fields around the black hole. If these magnetic fields wobbled somehow, it could cause a large burst of X-rays. In fact, such events are seen regularly on our own Sun, we call them solar flares.

The main part of this picture shows the area around the supermassive black hole at the center of our Galaxy, called Sagittarius A* (pronounced as "SAJ-ee-TARE-ee-us A-star"). The small box shows a close up of the black hole and the giant flare from 2013.
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(NASA/CXC/April Jubett)

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3. Tour of Sagittarius A*
QuicktimeMPEG Since NASA's Chandra X-ray Observatory was launched over 15 years ago, it has frequently turned its gaze to the center of the Milky Way galaxy. One of the reasons is that at the center of our Galaxy there is a black hole, which astronomers now estimate contains about four and a half million times the mass of the Sun. This makes this object, called Sagittarius A*, the closest supermassive black hole to us. Over the years, astronomers have learned many things about Sagittarius A* and it continues to surprise and intrigue scientists to this day. On September 13, 2013, astronomers saw a flare from Sagittarius A* that was 400 times brighter than its usual X-ray output. A little more than a year later, astronomers again used Chandra to see another flare from Sagittarius A* that was 200 times brighter than its normal state in October 2014.

What's going on with the Milky Way's biggest black hole? Astronomers have two theories about what could be causing these "megaflares" from Sagittarius A*. The first idea is that the intense gravity around the black hole ripped apart an asteroid that wandered too close. As the asteroid's debris swirled around the black hole, it would have been heated to temperatures that cause it to emit X-rays before passing over the edge of the black hole. The other proposed explanation involves the strong magnetic fields that exist around Sagittarius A*. If the magnetic field lines reconfigured themselves and reconnected, this could also create a large burst of X-rays. Scientists see flares happen regularly on the Sun and the events around Sgr A* appear to have a similar pattern in intensity levels to those. Whatever the final explanation is for these flares, scientists will continue to observe Sagittarius A* with Chandra and will undoubtedly make more fascinating discoveries about our Galaxy’s supermassive black hole.
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(NASA/CXC/A. Hobart)

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4. Tour of Sagittarius A*
QuicktimeMPEG One of the biggest mysteries in astrophysics today is figuring out where mysterious particles called neutrinos come from. Neutrinos are tiny particles that carry no charge and interact very weakly with electrons and protons. Unlike light or charged particles, neutrinos can emerge from deep within their sources and travel across the universe without being absorbed by intervening matter or, in the case of charged particles, deflected by magnetic fields.

The Earth is constantly bombarded with neutrinos from the sun. However, neutrinos from beyond the solar system can be millions or billions of times more energetic. Scientists have long been searching for the origin of these very energetic neutrinos.

Now scientists have a new clue in their hunt for the source of neutrinos. By analyzing data from three X-ray telescopes, including Chandra, researchers have found a connection between flares generated by the supermassive black hole at the center of the Milky Way and the arrival of high-energy neutrinos at a detector under the South Pole. In fact, the facility in Antarctica, called the IceCube Neutrino Observatory, saw one of these high-energy neutrinos less than three hours after Chandra detected the largest flare ever from the Milky Way's supermassive black hole. The Swift and NuSTAR X-ray telescopes also recorded flares that were later tied to IceCube neutrino detections.

While it's too early to say if the Milky Way's black hole is definitively generating high-energy neutrinos, the latest results are a promising lead for scientists to follow.
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(NASA/CXC/A. Hobart)

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5. Tour of Sagittarius A*
QuicktimeMPEG Jets of high-energy particles are found throughout the Universe on large and small scales. They are produced by young stars and by giant black holes. Jets play important roles in transporting energy away from the central object and, on a galactic scale, in regulating the rate of formation of new stars.

Because of that, astronomers have been searching for decades for a jet from the Milky Way's black hole known as Sagittarius A*. Over the years, there have been several reports of hints of a jet from Sgr A*, but none was conclusive. A new study involving data from NASA's Chandra X-ray Observatory and the Very Large Array, however, has provided the best case yet for a jet from our Galaxy's supermassive black hole.

One piece of evidence is a straight line of X-rays that points to Sgr A*. Another is the discovery of a shock front - akin to a sonic boom - seen in radio data, where the jet appears to be striking a cloud of gas. By combining these clues with other information, astronomers think they have the strongest evidence to date for a jet blasting out of Sgr A*. The likely discovery of a jet from Sgr A* helps astronomers learn more about the giant black hole, including how it is spinning.
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(NASA/CXC/April Jubett)

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6. Beyond the Horizon

For a long time people believed that the Earth was flat and that if you sailed too far you'd fall over the edge! It seems funny they could have thought that, because now we're lucky enough to have pictures of our entire planet and we can see its shape (take a look at image 2). But it took some pretty impressive technology to get these pictures, which wasn't available to our ancient ancestors. Did you know you have to travel about 20,000 kilometres from Earth to be able to see the entire planet?

Now imagine how far into space you'd have to travel to fit all the 300 billion stars of the Milky Way (our Galaxy) into one shot! This is way beyond our abilities at the moment, but we can photograph small sections of the Galaxy. This picture from the Chandra X-ray Observatory shows the very centre of the Milky Way. This is the most chaotic and dangerous part of the Galaxy, and home to a supermassive black hole.

Anything that gets too close to a black hole is pulled into it with such a strong force that it has no chance of escape. The boundary that marks the point of no return is called the event horizon. Past this not even light will return: this monster will pull it in forever. The blue haze in this picture includes piping-hot gas floating perilously close to the event horizon of our Galaxy's supermassive black hole. But astronomers have found that just a tiny amount of this gas will be gobbled up by the black hole, and the rest will be "spat out" before it gets too close.

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(NASA/CXC/April Jubett)

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7. Learn About the Milky Way
QuicktimeMPEG The word galaxy comes from the Greek word meaning "milky circle" or the more familiar Milky Way.
The white band of light across the night sky that we call the Milky Way was poetically described long before Galileo, but with his small telescope, what he discovered was a multitude of individual stars, so numerous as almost to surpass belief.
Today we know that the Milky Way is our home galaxy, a vast rotating spiral of gas, dust and hundreds of billions of stars.
The sun and its planetary system formed in the outer reaches of the Milky Way about 4.5 billion years ago.
See the Milky Way through Chandra's eyes.
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(NASA/CXC/A. Hobart)

Click for high-resolution animation
8. Tour of Sagittarius A*
QuicktimeMPEG Over several years, astronomers have noticed flares in X-ray light from the black hole at the center of the Milky Way. NASA's Chandra X-ray Observatory detected these flares during the telescope's periodic observations of the black hole. A new study suggests that these flares may occur when the black hole - known as Sagittarrius A* or Sgr A* for short -- consumes an asteroid at least six miles wide. If an asteroid gets too close to another object like a star or planet, it can be thrown into an orbit headed toward Sgr A*. Once the asteroid passes within about 100 million miles of the black hole, it is torn into pieces by the black hole's tidal forces. Eventually, these fragments are vaporized by friction as they pass through the hot, thin gas flowing onto Sgr A*. This is what produces an X-ray flare. If confirmed, this result could mean that there is a cloud around Sgr A* containing trillions of asteroids and comets. This would be an exciting development for the many scientists who are fascinated by the Milky Way's giant black hole and the environment around it.
[Runtime: 01:17]
(NASA/CXC/A. Hobart)

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9. Animation of a Black Hole's Outburst
QuicktimeMPEG This animation shows how high-energy particles and X-ray flares are produced when matter falls onto the accretion disk around a supermassive black hole. Astronomers believe such an event occurred to produce the light echo seen in the latest Chandra results.
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10. Illustrations of Light Echo
QuicktimeMPEG This sequence of illustrations shows how an outburst from Sgr A* -- produced when material falls into the black hole -- generates a light echo. The faint, star-like object in the center represents the typical, quiet behavior, when the black hole does not have much material to consume. When the black hole's feeding rate increases dramatically, the material around Sgr A* brightens. Although the black hole outburst stops, the light from the outburst continues to travel outwards and then reflects, or echoes, off three clouds of gas in its path.
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