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-------------------------- 2461 - BLACKHOLES - first discoveries?
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- Astronomers can often only spot black holes that are in binary pairs with stars in which the black hole orbits and siphons matter from the star. This is because, when black holes accrete matter from their partner star, they emit bright, easy-to-spot X-rays.
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- Many black holes in these pairings don't orbit their star close enough to accrete mass and emit this bright signal, so they go undetected.
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- This year, 2019, they looked at a binary star system made up of the giant star 2MASS and a companion, which they found is likely a low-mass black hole.
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- To find the hidden black hole, the astronomers began by poring through data from APOGEE, a survey that uses spectroscopy data to scour the sky for stars. After observing over 100,000 stars, the team identified which stars had significant Doppler shift, or redshift and blueshift.
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- Redshift occurs when the wavelengths of light coming from objects moving away from Earth get longer, and the object appears red. Blueshift occurs when the wavelengths of light coming from objects moving closer, shorten, and the object appears blue.
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- The team combined data on stars exhibiting Doppler shift with data from the All-Sky Automated Survey for Supernovae (ASAS-SN) project, in which robotic telescopes worldwide monitor the night sky and collect data on millions of stars. With this data, scientists can see the brightness of stars over time.
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- The researchers whittled down the list of stars to those that showed the most extreme Doppler shift. They looked at the stars' light curves, or how the brightness of those stars changed over time in the ASAS-SN data. The combination of those two factors led astronomers to this one particular star, this giant star in the outer galaxy, 2MASS
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- The star's brightness kept changing, brightening and dimming back and forth. The team confirmed that the brightness variations were in line with the orbital period of an object orbiting the star.
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- When they studied the system further, the researchers determined that the object must have a mass of around 3.3 solar masses, ranging from 2.6 to 6.1 solar masses. This mass is consistent with a low-mass black hole.
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- Identifying this black hole which, because it doesn't emit bright X-rays, had previously escaped detection by astronomers, is an important step forward in allowing researchers to more easily identify these type of "hidden" black holes.
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- This black hole is approximately 3.3 times the mass of the Sun. That makes it much less massive than black holes in bright, X-ray-emitting systems, which are usually five to six solar masses.
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- It's also less massive than black holes that merge across the universe in gravitational waves, which are often 20 to 30 solar masses. If this object is found to have the lowest mass deemed possible in its margin or error, it could turn out to be a neutron star at its maximum mass.
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- If this object is closer to the upper range of its estimated mass, it would add to the definition of what qualifies as a black hole. If the black hole is, in fact, 3.3 solar masses it will provide evidence for the assumption that there are possibly plenty of black holes in the cosmos that don't emit X-rays.
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- Normally we think of black holes as gigantic cosmic monsters, exotic objects whose gravity is so strong that not even light can escape their clutches. But, black holes can come in a wide variety of forms, from small stellar-mass bodies to the supermassive beasts that reside at the hearts of galaxies.
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- Nearly all galaxies are thought to harbor at their cores supermassive black holes millions to billions of times the mass of our Sun.
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- Galaxies, NGC 3842, the brightest galaxy in the Leo cluster nearly 320 million light years away, has a central black hole containing 9.7 billion solar masses. In another galaxy , NGC 4889, the brightest galaxy in the Coma cluster more than 335 million light years away, has a black hole of likely larger mass.
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- The gravitational range, or "event horizon," of these black holes is about five times the distance from the Sun to Pluto. For comparison, these black holes are 2,500 times as massive as the black hole at the center of our Milky Way galaxy, whose event horizon is one-fifth the orbit of Mercury.
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- Another binary star system may contain the smallest black hole known. Scientists discovered it by studying the heartbeat-like pattern of X-rays thought to be emitted from a disk of accreting matter around the black hole.
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- This smallest black hole discovered to date may be less than three times the mass of our Sun. This would put this little monster near the theoretical minimum limit needed for a black hole to be stable. As tiny as this black hole may be, it is capable of 20 million mph winds, the fastest yet observed from a stellar-mass black hole by nearly 10 times.
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- Black holes devour anything unlucky enough to drift too close, including other black holes. Scientists recently detected the monstrous black hole at the heart of one galaxy getting consumed by a still larger black hole in another.
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- The discovery is the first of its kind. Astronomers had witnessed the final stages of the merging of galaxies of equal mass, but, minor mergers between galaxies and smaller companions had long eluded researchers.
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- Using NASA's Chandra X-ray Observatory, investigators detected two black holes at the center of a galaxy, NGC3393, with one black hole about 30 million times the mass of the Sun and the other at least 1 million times the mass of the Sun, separated from each other by only about 490 light-years.
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- Black holes are known for sucking in matter, but researchers find they can shoot it out as well. Observations of a black hole, H1743-322, which harbors 5 to 10 times the mass of the Sun and is located about 28,000 light-years from Earth, revealed it apparently pulled matter off a companion star, then spat some of it back out as gigantic "bullets" of gas moving at nearly a quarter the speed of light.
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- The oldest black hole found was born about 770 million years after the Big Bang that created our universe. The Big Bang occurred about 13,700 million years ago.
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- The ancient age of this black hole actually poses some problems for astronomers. This brilliant object appears to be 2 billion times the mass of the Sun. How these black holes became so massive so soon after the Big Bang is difficult for astronomers to explain.
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- Although the gravitational pulls of black holes are so strong that even light cannot escape, they also make up the heart of quasars, the most luminous, most powerful and most energetic objects in the universe.
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- As supermassive black holes at the centers of galaxies suck in surrounding gas and dust, they can spew out huge amounts of energy. The brightest quasar we see in the visible range is 3C 273, which lies about 3 billion light-years away.
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- When galaxies collide, black holes can get kicked away from the site of the crash to roam freely through space. The first known of these rogue black holes may be approximately 600 million times the mass of the Sun and hurtling through space at 5,900,000 mph. Hundreds of rogue these black holes might be wandering the Milky Way.
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- Astronomers have long thought that black holes come in three sizes small, medium and large. Relatively small black holes holding the mass of a few suns are common, while supermassive black holes millions to billions of solar masses are thought to lurk at the heart of nearly every galaxy. One more massive than four million suns, for example, is thought to hide in the center of the Milky Way.
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- However, middle-weight black holes had eluded astronomers for years. Astronomers recently discovered an intermediate-mass black hole, HLX-1, approximately 290 million light-years from Earth, which appears to be about 20,000 solar masses in size.
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- Medium-size black holes are thought to be the building blocks of supermassive black holes, so understanding more about them can shed light on how these monsters and the galaxies that surround them evolved.
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- Black holes can whirl the fabric of space around themselves at extraordinary speeds. One black hole in the constellation Aquila (The Eagle) about 35,000 light-years from Earth, is spinning more than 950 times per second.
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- Anything placed on the edge of the black hole's event horizon, the edge past which nothing can escape, would spin around it at a speed of more than 333 million mph, or about half the speed of light.
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- Black holes possess gravitational pulls so powerful that nothing, including light, can escape after falling past a border known as the event horizon. Scientists have created an artificial event horizon in the lab using fiber optics. They have also recreated the so-called Hawking radiation thought to escape from black holes.
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- We keep learning more about these mysterious objects that exit at the edge of known physics. Stay tuned, new discoveries are just around the corner of our knowledge. Astronomy is awesome.
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- November 2, 2019
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