Category Archives: x-ray astronomy

black holes, x-ray astronomy

11.5 Weeks to Black Holes in the Distant Universe

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X-rays From Black Holes Reveal Growth Over Time

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This image contains the highest concentration of black holes ever seen, equivalent to 5,000 over the area of the full Moon. CXC.

What do you think you could find if you pointed an extremely sensitive x-ray telescope toward a distant part of the sky for nearly three weeks? That’s the challenge that Chandra X-ray Telescope scientists took on. The result is the image on the left.

This highly detailed view was produced by the observatory and gives astronomers the best look yet at the growth of black holes over billions of years beginning soon after the Big Bang.

This is the deepest x-ray image ever obtained. It comes from what is known as the Chandra Deep Field-South study. The central region of the image contains the highest concentration of supermassive black holes ever seen. The observations, which began in 1999 and continued into 2016, totaled more than 7 million seconds of telescope time. What those 11.5 weeks of total time covers an astonishing depth of study that stretches back through 12.5 billion years of time.

Using X-rays to Trace Black Holes

The image explores the earliest days of black holes in the universe. About 70% of the objects in the new image are supermassive black holes and it’s so rich that it allows scientists to see change over time.

How can black holes emit x-rays? Gas falling towards these black holes becomes much hotter as it approaches the event horizon/ That superheating results in bright x-ray emission. And, tracing those emissions is what gives astronomers new insights about the types and sizes of black holes nurtured by the early cosmos and their rates of growth.

How Does the Black Hole Garden Grow?

The growth of black holes in the early universe is a huge topic of scientific interest. Deep x-ray studies give astronomers a good idea about their evolution back “in the day”. It turns out that black holes grew mostly in bursts rather than slowly gobbling up material over time to get bigger in the epoch just after the Big Bang.

The x-ray emissions from these massive objects also help astronomers understand something about the “seeds” they grew from. It turns out that they may have started out with masses about 10,000 to 100,000 times that of the Sun, rahter than as really small black holes of just a few hundreds of solar masses. Moreover, they appear to have grown very rapidly to more than a billion solar masses very early on.

Black Holes as Far as They Can “See”

The researchers also detected x-rays from massive galaxies at distances up to about 12.5 billion light-years from Earth. Most of the x-ray emission from these distant galaxies likely comes from large collections of stellar-mass black holes within them. They formed from the collapse of massive stars and typically weigh a few to few dozen times the mass of the Sun.

How They Observed The X-Ray Deep Field

The team combined Chandra x-ray data with very deep Hubble Space Telescope data over the same patch of sky. They studied x-ray emission from more than 2,000 galaxies identified by Hubble that are located between about 12 and 13 billion light-years from Earth.

What’s Next?

Chandra and future x-ray observatories will be needed to provide a definite solution to the mystery of just how supermassive black holes grew to reach their current massive states. Now that the deep field has shown the way, astronomers will take much larger samples of distant galaxies using the James Webb Space Telescope. That will give even more targets for x-ray sensitive observatories to observe further out in space and back in time.

asteroid, black hole, Sgr A*, x-ray astronomy

Black Hole Munches Asteroids

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Is There No End to Its Incessant Demands?

This image from NASA's Chandra X-ray Observatory shows the center of our Galaxy, with a supermassive black hole known as Sagittarius A* (Sgr A* for short) in the center. Using intermittent observations over several years, Chandra has detected X-ray flares about once a day from Sgr A*. The flares have also been seen in infrared data from ESO's Very Large Telescope in Chile. Click to embiggen.

How did I miss this story?  Early in February, the folks working with the Chandra X-ray Observatory announced that they’ve been watching the black hole at the heart of the Milky Way Galaxy munching down on asteroids.  According to them, this happens pretty frequently. They’ve seen the evidence:  once-a-day x-ray flares from Sagittarius A* (that’s the name given to our central black hole), or Sgr A* for short. The flares last a few hours, and have also been seen in infrared light by detectors at the Very Large Telescope in Chile.

The idea is that there is a cloud around Sgr A* containing hundreds of trillions of asteroids and comets. Where did they come from? Astronomers suggest that this debris collection is made of material stripped from the parent stars by the force of gravity.

An asteroid that gets too close to  another object, such as a star or planet, can get thrown into an orbit that places it on a heading for  Sgr A*.  If it gets too close — say within 100 million miles of the black hole (about the distance between Earth and the Sun) it would be torn into pieces as it encountered the  tidal forces from the black hole. These fragments would be vaporized as they pass through the hot, thin gas that continually flows toward Sgr A*.  This is very similar to what happens to a meteor when it encounters Earth’s atmosphere for example. It heats up and glows, and eventually it vaporizes, and we see a flare marking the end of the meteor’s trip. When an object does this near Sgr A*, we can see it in x-rays and infrared.  Whatever’s left of the asteroid gets sucked into the black hole.

This is kind of a cool thing to see at an object so far away, and Chandra’s still on the case. Over the next year or so, the satellite will study more of these things that go “fuff” in the night near Sgr A*.