ESA steps towards a great black hole censusSeptember 07, 2006
Astronomers using ESA's orbiting gamma-ray observatory, Integral, have taken an important step towards estimating how many black holes there are in the Universe.
An international team, lead by Eugene Churazov and Rashid Sunyaev, Space Research Institute, Moscow, and involving scientists from all groups of the Integral consortium used the Earth as a giant shield to watch the number of tell-tale gamma rays from the distant Universe dwindle to zero, as our planet blocked their view. "Point Integral anywhere in space and it will measure gamma rays," says Pietro Ubertini, INAF, Italy and Principal Investigator on Integral's gamma-ray imager. Most of those gamma rays do not come from nearby sources but from celestial objects so far away that they cannot yet be distinguished as individual sources. This distant gamma-ray emission creates a perpetual glow that bathes the Universe.
Most astronomers believe that the unseen objects are supermassive black holes, millions or billions of times heavier than the Sun and each sitting at the centre of a galaxy. As the black holes swallow matter, the swirling gases release X-rays and gamma rays. Accurately measuring the glow, known as the X-ray and gamma-ray background, is the first step towards calculating how many black holes are contributing to it and how far away in the Universe they are located.
The new Integral observations were made during January and February 2006 and provide highly accurate data on the gamma-ray background. The key to success was using the Earth as a shield.
Allowing the Earth to enter Integral's field of view goes against the standard set of nominal observations for the satellite, because the optical devices needed to determine the spacecraft's attitude would be blinded by the bright Earth. So, this operation required remarkable efforts from the ISOC/MOC teams operating the mission, who had to rely on alternative spacecraft control mechanisms. But the risk was worth it: by measuring the decrease of the gamma-ray flux once the Earth had blocked Integral's view and by making a model of the Earth's atmospheric emission, the astronomers precisely gauged the gamma-ray background.
Another bonus of the Integral observations is that the observatory's complementary instruments allowed the strength of both X-rays and gamma rays to be measured simultaneously. In the past, different satellites have had to measure the different energies of X-rays and gamma rays, leaving astronomers with the task of having to piece the results together like the pieces of a jigsaw puzzle.
It is not just the overall glow that Integral has seen. Before the satellite's launch, only a few dozen celestial objects were observed in gamma rays. Now Integral sees about 300 individual sources in our Galaxy and around 100 of the brightest supermassive black holes in other galaxies. These are the tip of the iceberg. Astronomers believe there are tens of millions of active black holes spread throughout space, all contributing to the gamma-ray background. From earlier observations in the softer X-ray band it is known that the soft background radiation is almost entirely populated by Active Galactic Nuclei (AGN). So it is highly likely that these objects are also responsible here at higher Integral energies, even if this is not proven yet.
The next step is for astronomers to programme computer models to calculate how the emission from this unseen population of black holes merges to give the observed glow. These computer models will predict the number and distance of the black holes, and provide insights into the way they behave at the centre of young, middle-aged and old galaxies. Meanwhile, the Integral team will continue to refine their measurements of the perplexing gamma-ray background.
For more information on these findings see: "Integral observations of the cosmic X-ray background in the 5-100 keV range via occultation by the Earth"
(http://www.arxiv.org/abs/astro-ph/0608250), by Churazov et al.; "Hard X-ray emission of the Earth's atmosphere: Monte Carlo simulations"
(http://www.arxiv.org/abs/astro-ph/0608253), by Sazonov et al.; "Earth X-ray albedo for CXB radiation in the 1-1000 keV band"
(http://www.arxiv.org/abs/astro-ph/0608252), by Churazov et al.
European Space Agency
Related Black Holes Articles:
U astronomers and colleagues have found two ultra-compact dwarf galaxies with supermassive black holes, the second and third such galaxies found to harbor the objects.
Observations using ESO's Very Large Telescope have revealed stars forming within powerful outflows of material blasted out from supermassive black holes at the cores of galaxies.
After the first direct detection of gravitational waves that was announced last February by the LIGO Scientific Collaboration and made news all over the world, Luciano Rezzolla (Goethe University Frankfurt, Germany) and Cecilia Chirenti (Federal University of ABC in Santo André, Brazil) set out to test whether the observed signal could have been a gravastar or not.
Computer simulations of a spherical collection of stars known as 'NGC 6101' reveal that it contains hundreds of black holes, until now thought impossible.
The NuSTAR mission is identifying which black holes erupt with the highest-energy X-rays.
Binary black holes recently discovered by the LIGO-Virgo collaboration could be primordial entities that formed just after the Big Bang, report Japanese astrophysicists.
Data from a now-defunct satellite is providing new insights into the complex tug-of-war between galaxies, the hot plasma that surrounds them, and the giant black holes that lurk in their centers.
Scientists from MIPT, the Institute for Theoretical and Experimental Physics, and the National Research University Higher School of Economics have devised a method of distinguishing black holes from compact massive objects that are externally indistinguishable from one another.
Black holes are the most powerful gravitational force in the universe.
The supermassive black holes found at the center of every galaxy, including our own Milky Way, may, on average, be smaller than we thought, according to work led by University of Southampton astronomer Dr.
Related Black Holes Reading:
The Little Book of Black Holes (Science Essentials)
by Steven Gubser (Author), Frans Pretorius (Author)
Dive into a mind-bending exploration of the physics of black holes
Black holes, predicted by Albert Einstein’s general theory of relativity more than a century ago, have long intrigued scientists and the public with their bizarre and fantastical properties. Although Einstein understood that black holes were mathematical solutions to his equations, he never accepted their physical reality―a viewpoint many shared. This all changed in the 1960s and 1970s, when a deeper conceptual understanding of black holes developed just as new observations revealed the existence of quasars... View Details
Black Holes and Time Warps: Einstein's Outrageous Legacy (Commonwealth Fund Book Program)
by Kip S. Thorne (Author), Stephen Hawking (Foreword)
Winner of the 2017 Nobel Prize in Physics
Ever since Albert Einstein's general theory of relativity burst upon the world in 1915 some of the most brilliant minds of our century have sought to decipher the mysteries bequeathed by that theory, a legacy so unthinkable in some respects that even Einstein himself rejected them.
Which of these bizarre phenomena, if any, can really exist in our universe? Black holes, down which anything can fall but from which nothing can return; wormholes, short spacewarps connecting regions of the cosmos; singularities, where... View Details
A Black Hole Is Not a Hole
by Carolyn Cinami DeCristofano (Author), Michael Carroll (Illustrator)
Budding astronomers and scientists will love this humorous introduction to the extremely complex concept of black holes. With space facts and answers about the galaxies (ours, and others) A Black Hole is NOT a Hole takes readers on a ride that will stretch their minds around the phenomenon known as a black hole.
In lively and text, the book starts off with a thorough explanation of gravity and the role it plays in the formation of black holes. Paintings by Michael Carroll, coupled with real telescopic images, help readers visualize the facts and ideas presented in the... View Details
Death by Black Hole: And Other Cosmic Quandaries
by Neil deGrasse Tyson (Author)
“[Tyson] tackles a great range of subjects . . . with great humor, humility, and―most important― humanity.” ―Entertainment WeeklyLoyal readers of the monthly "Universe" essays in Natural History magazine have long recognized Neil deGrasse Tyson's talent for guiding them through the mysteries of the cosmos with clarity and enthusiasm. Bringing together more than forty of Tyson's favorite essays, ?Death by Black Hole? explores a myriad of cosmic topics, from what it would be like to be inside a black hole to the movie industry's... View Details
Black Holes: A Very Short Introduction (Very Short Introductions)
by Katherine Blundell (Author)
Black holes are a constant source of fascination to many due to their mysterious nature. This Very Short Introduction, addresses a variety of questions, including what a black hole actually is, how they are characterized and discovered, and what would happen if you came too close to one.
Professor Katherine Blundell looks at the seemingly paradoxical, mysterious, and intriguing phenomena of black holes. Outlining their nature and characteristics, both those resulting from the spectacular collapse of heavy stars, and the giant black holes found at the centres of galaxies, she... View Details
Black Holes (A True Book)
by Ker Than (Author)
Describes how black holes form, their different sizes, how scientists find black holes in space, and if anything can escape from its gravitational pull. View Details
Black Holes (Kindle Single)
The legendary physicist explores his favorite subject in a pair of enlightening, accessible, and cleverly illustrated essays for curious readers, originally delivered as BBC lectures.
“It is said that fact is sometimes stranger than fiction, and nowhere is that more true than in the case of black holes. Black holes are stranger than anything dreamed up by science-fiction writers, but they are firmly matters of science fact.”
For decades, Stephen Hawking has been fascinated by black holes. He believes that if we understood the challenges they... View Details
Black Hole (Pantheon Graphic Novels)
by Charles Burns (Author)
Winner of the Eisner, Harvey, and Ignatz Awards
The setting: suburban Seattle, the mid-1970s. We learn from the outset that a strange plague has descended upon the area’s teenagers, transmitted by sexual contact. The disease is manifested in any number of ways — from the hideously grotesque to the subtle (and concealable) — but once you’ve got it, that’s it. There’s no turning back.
As we inhabit the heads of several key characters — some kids who have it, some who don’t, some who are about to get it — what unfolds isn’t the expected battle to fight... View Details
Black Hole Blues and Other Songs from Outer Space
by Janna Levin (Author)
The authoritative story of Rainer Weiss, Barry Barish, and Kip Thorne’s Nobel Prize–winning discovery of gravitational waves—by an eminent theoretical astrophysicist and award-winning writer.
With A New Preface
In 1916, Einstein predicted the presence of gravitational waves. One century later, we are recording the first sounds from space, evidence of the waves’ existence caused by the collision of two black holes. An authoritative account of the headline-making discovery by theoretical astrophysicist and award-winning writer Janna Levin, Black Hole Blues... View Details
Black Hole: How an Idea Abandoned by Newtonians, Hated by Einstein, and Gambled On by Hawking Became Loved
by Marcia Bartusiak (Author)
The contentious history of the idea of the black hole—the most fascinating and bizarre celestial object in the heavens
For more than half a century, physicists and astronomers engaged in heated dispute over the possibility of black holes in the universe. The weirdly alien notion of a space-time abyss from which nothing escapes—not even light—seemed to confound all logic. This engrossing book tells the story of the fierce black hole debates and the contributions of Einstein and Hawking and other leading thinkers who completely altered our view of the universe.