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Recent Podcast
A Tour of V745 SCO
A Tour of V745 SCO
For decades, astronomers have known about irregular outbursts from the double star system V745 Sco, which is located about 25,000 light years from Earth. (2017-09-19)
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Animations & Video: Featured Image Tours
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1. Tour of PSR B1259-63/LS 2883
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

In astronomy, it is often difficult to figure out exactly far away objects are. For objects in our Solar System and nearby stars, astronomers can use reliable methods involving geometry. However, these techniques cannot be applied to objects beyond our immediate cosmic neighborhood. There are some rare circumstances where relatively simple geometric techniques can be used to determine distances to more far-flung objects.

This is the case of Circinus X-1, a system in which a neutron star is in orbit around a massive star. In 2013, astronomers watched as Circinus X-1 erupted in a giant burst of X-rays. Afterwards, they used NASA's Chandra X-ray Observatory and ESA's XMM-Newton to observe what happened next. The scientists now report that they see a set of four rings that appear as circles around Circinus X-1. What are these are these rings and what do they do? These rings are light echoes, similar to sound echoes that we may experience here on Earth. Instead of sound waves bouncing off a canyon wall, the echoes around Circinus X-1 are produced when a burst of X-rays from the star system ricochets off of clouds of dust between Circinus X-1 and Earth.

By combining the light echoes that Chandra detects with radio data from the Mopra telescope in Australia, which determined the distance to the intervening clouds, astronomers can estimate the distance to Circinus X-1 using relatively simple geometry. The light echo method generates a distance of 30,700 light years. The observation thus settles a large difference amongst previous results, one similar to this work and one indicating a much smaller distance of about 13,000 light years.
[Runtime: 02:06]
(NASA/CXC/A. Hobart)

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2. Tour of RGG 118
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

Oxymorons are often thought of as gaffes in language, but a new black hole discovery shows they can also represent important scientific advances. Astronomers using NASA's Chandra X-ray Observatory and the 6.5-meter Clay Telescope in Chile have identified the smallest giant black hole known. This oxymoronic object could provide clues to how much larger black holes formed along with their host galaxies billion of years in the past.

Astronomers estimate this supermassive black hole is about 50,000 times the mass of the Sun. This is less than half the previous lowest mass for a black hole at the center of a galaxy. The tiny heavyweight black hole is located at the center of a dwarf disk galaxy, called RGG 118, about 340 million light years from Earth.

Researchers estimated the mass of the black hole by studying the motion of cool gas near the center of the galaxy using visible light data from the Clay Telescope. They used the Chandra data to figure out the brightness in X-rays of hot gas swirling toward the black hole. They found that the outward push of radiation pressure of this hot gas is about 1% of the black hole's inward pull of gravity. This matches the properties of other supermassive black holes.

The black hole in RGG 118 is nearly 100 times less massive than the supermassive black hole found in the center of the Milky Way. It is also about 200,000 times less massive than the heaviest black holes found in the centers of other galaxies.

Researchers will keep looking for other supermassive black holes that are comparable in size or even smaller than the one in RGG 118. It is important to gather a large sample because black holes of this size might be seeds that lead to the formation of much larger supermassive black holes.
[Runtime: 02:10]
(NASA/CXC/A. Hobart)

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3. Tour of Sagittarius A*
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

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.
[Runtime: 02:30]
(NASA/CXC/A. Hobart)

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4. Tour of SDSS J103842.59+484917.7
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

One hundred years ago this month, Albert Einstein published his theory of general relativity, one of the most important scientific achievements in the last century. A key result of Einstein's theory is that matter warps space-time. This means that a massive object can bend the light we see on Earth from very distant objects, say, faraway galaxies. Astronomers have found many examples of this phenomenon, known as "gravitational lensing." Gravitational lensing is more than just a cosmic illusion, however. Instead, gravitational lensing provides astronomers with a way of probing extremely distant galaxies and groups of galaxies in ways that would otherwise be impossible even with the most powerful telescopes.

The latest results from the "Cheshire Cat" group of galaxies show how manifestations of Einstein's 100-year-old theory can lead to new discoveries today. Astronomers have given the group this name because to many it looks like a smiling cat from the famous story of "Alice in Wonderland." In a twist that perhaps Lewis Carroll could appreciate, some of the feline features in this cosmic Cheshire Cat are actually distant galaxies whose light has been stretched and bent by the large amounts of mass in the system.

Astronomers have studied the Cheshire Cat in optical light from telescopes like the Hubble Space Telescope and the Gemini Observatory on Mauna Kea. They have also used the Chandra X-ray Observatory to study it in higher-energy light. X-rays from Chandra reveal gas in between the galaxies that has been heated to millions of degrees. This superhot gas is evidence that the two eyes of the Cheshire Cat, and the small galaxies associated with them, are racing toward one another at very high speeds. In fact, astronomers estimate that these galaxies will merge in about one billion years. X-ray data also show that the left "eye" of the Cheshire Cat group contains an actively feeding supermassive black hole at the center of the galaxy. Scientists will continue to study this system and others like it to explore all of the ways Einstein's theory from a century ago helps explain our view of the Universe today.
[Runtime: 03:14]
(NASA/CXC/A. Hobart)

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5. Tour of SGR 1745-2900
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

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.
[Runtime: 02:14]
(NASA/CXC/April Jubett)

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6. Tour of SgrA
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

At the heart of the Milky Way galaxy, there is a supermassive black hole that has the mass equivalent of some four million Suns. Astronomers think that nearly every galaxy has such a black hole at its center. For reasons that scientists don't fully understand, the Milky Way's black hole - known as Sagittarius A* -- is unusually quiet compared to similarly sized black holes in other galaxies. Recently, however, there was a change in the behavior of Sagittarius A*. This was discovered thanks to a long-term monitoring campaign of the black hole by three orbiting X-ray telescopes: NASA's Chandra X-ray Observatory, ESA's XMM-Newton, and NASA's Swift Gamma Ray Burst Explorer. Since 1999, these telescopes in space have periodically observed Sagittarius A*.

While things have been relatively quiet from the black hole over most of the past decade and a half, astronomers saw an increase in flares in the middle of 2014. This was several months after scientists predicted a dusty object, called G2, would be making a close approach to the black hole. It's possible that G2 got so close that the strong gravitational pull of black hole grabbed some of its dust, sending it down toward the black hole and heating it up to temperatures where it glowed in X-rays. While the timing is intriguing, it's not an open and shut case. For example, the uptick of X-rays could be the result of a change in the strength of winds from nearby massive stars that are feeding the black hole. Astronomers will continue to observe Sagittarius A* with Chandra and other telescopes and hope that additional data will shed light on the questions surrounding our Galaxy's supermassive black hole.
[Runtime: 02:14]
(NASA/CXC/A. Hobart)

Related Chandra Images:

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7. Tour of Space-time Foam
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

At the smallest scales of distance and duration that we can measure, space-time - that is, the three dimensions of space plus time - appears to be smooth and structureless. Think of flying over the ocean in an airplane. From 30,000 feet or so, the ocean appears completely smooth. However, if your plane were to descend low enough, you could make out the waves and swells of the water. Certain aspects of quantum mechanics, the highly successful theory scientists have developed to explain the physics of atoms and subatomic particles, predict that space-time may act the same way. Instead of being totally smooth, it would have a foamy, jittery nature if we could look at small enough scales -- like those waves on the ocean. In these models, space-time would consist of many small, ever-changing, regions for which space and time are constantly fluctuating.

Since space-time foam, as it is called, is so tiny, scientists cannot observe it directly. However, they can hunt for evidence for its existence - or non-existence - in things we can see. By looking at the light from distant quasars in X-rays from Chandra as well as gamma-ray telescopes, a team of scientists set out to test some of the models of space-time foam.

What did they find? The researchers say their evidence can help rule out two different models of space-time foam. While their work does not eliminate the existence of space-time foam entirely, it does suggest that space-time is less foamy than some models predict. Scientists will continue to test the nature of space and time on the very smallest scales using every experiment they can think of, including using high-energy light from across the Universe.
[Runtime: 02:02]
(NASA/CXC/A. Hobart)

Related Chandra Images:

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8. Tour of Zwicky 8338
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

An extraordinary ribbon of hot gas trailing behind a galaxy like a tail has been discovered using data from NASA's Chandra X-ray Observatory. This ribbon, or X-ray tail, is likely due to gas stripped from the galaxy as it moves through a vast cloud of hot intergalactic gas. With a length of at least 250,000 light years, it is likely the largest such tail ever detected.

The tail is located in the galaxy cluster Zwicky 8338, which is almost 700 million light years from Earth. The length of the tail is more than twice the diameter of the entire Milky Way galaxy and contains gas with temperatures of about 10 million degrees.

Galaxy clusters are the largest structures in the Universe held together by gravity. They consist of hundreds, or even thousands, of galaxies, enormous pools of hot gas, and vast amounts of unseen dark matter. Since galaxy clusters are so enormous, they play a critical role inunderstanding how our Universe evolves. X-ray tails like the one in Zwicky 8338 show how the galaxies within a cluster can transform over time. This gives scientists important information in understanding these critical cosmic systems.
[Runtime: 02:19]
(NASA/CXC/A. Hobart)

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9. Tour of AM CVn
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

In the middle of the twentieth century, an unusual star was spotted in the constellation of Canes Venatici (Latin for "hunting dogs"). Years later, astronomers determined that this object, dubbed AM Canum Venaticorum (or, AM CVn, for short), was, in fact, two stars. These stars revolve around each other every 18 minutes, and are predicted to generate gravitational waves - ripples in space-time predicted by Einstein.

Today, the name AM CVn represents a class of objects where one white dwarf star is pulling matter from a very compact companion star, such as a second white dwarf. (White dwarf stars are dense remains of Sun-like stars that have run out of fuel and collapsed to the size of the Earth.) The pairs of stars in AM CVn systems orbit each other extremely rapidly, whipping around one another in an hour, and in one case as quickly as 5 five minutes. By contrast, the fastest orbiting planet in our Solar System, Mercury, orbits the Sun once every 88 days.

Despite being known for almost 50 years, the question has remained: where do AM CVn systems come from? New X-ray and optical observations have begun to answer that with the discovery of the first known systems of double stars that astronomers think will evolve into AM CVn systems.

Observations with optical telescopes on the ground helped identify two systems, known as J0751 and J1741, that contain two white dwarfs and determined their masses. Scientists used Chandra to help rule out the possibility that J0751 and J1741 contained neutron stars. A neutron star - which would disqualify it from being a possible parent to an AM CVn system - would give off strong X-ray emission due to its magnetic field and rapid rotation. No X-ray emission was seen from either system, thus convincing scientists that these were going to evolve into AM CVn in the future.

As we mentioned before, AM CVn systems are of interest to scientists because they are predicted to be sources of gravitational waves. This is important because even though such waves have yet to be detected, many scientists and engineers are working on instruments that should be able to detect them in the near future. This will open a significant new observational window to the universe.
[Runtime: 02:55]
(NASA/CXC/A. Hobart)

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10. Tour of DEM L241
QuicktimeMPEG Audio Only With closed-captions (at YouTube)

When a massive star runs out fuel, it collapses and explodes as a supernova. Although these explosions are extremely powerful, it is possible for a nearby star to endure the blast. A team of astronomers using NASA's Chandra X-ray Observatory and other telescopes has found evidence for one of these survivors. This hardy star is in a stellar explosion's debris field - also called its supernova remnant - located in an HII region called DEM L241. An HII (pronounced "H-two") region is created when the radiation from hot, young stars strips away the electrons from neutral hydrogen atoms to form clouds of ionized hydrogen. This particular HII region is located in the Large Magellanic Cloud, a small neighboring galaxy to the Milky Way. The supernova remnant remains hot for thousands of years after the original explosion occurred, and this means that it continues to glow brightly in X-rays that can be detected by Chandra. The data suggest that a point-like source in X-rays is one component of a binary star system. In such a celestial pair, either a neutron star or black hole, which is formed when the star went supernova, is in orbit with a star much larger than our Sun. As they orbit one another, the dense neutron star or black hole pulls material away its companion star through the wind of particles that flows away from its surface. If this result is confirmed, DEM L241 would be only the third binary containing both a massive star and a neutron star or black hole ever found in the aftermath of a supernova.
[Runtime: 01:59]
(NASA/CXC/A. Hobart)

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