Energy News  
ESA Steps Towards A Great Black Hole Census

This all-sky image was obtained by ESA's Integral gamma-ray observatory during four years of operations and provides an important step towards estimating how many black holes there are in the Universe. The sources in this image were artificially blurred and the colour map was stretched to make both strong and weak sources readily visible. The concentration of sources along the mid plane of the image is due to neutron stars and stellar mass black holes in our Galaxy, while the majority of sources located far away from the Galactic plane are super-massive black holes in other galaxies. The Cosmic X-ray Background is composed from the emission of tens of millions of similar objects much further away from us. Superposed is an Earth image by ESA/EUMETSAT's Meteosat satellite. Using the Earth as a shield to block the emission from the population of distant black holes astronomers precisely gauged the X-ray and gamma-ray background. An angular size of the Earth as seen from Integral during actual observations was smaller than shown in the image. Credits: ESA/IKI Integral team
by Staff Writers
Paris, France (ESA) Sep 08, 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 from 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.

Community
Email This Article
Comment On This Article

Related Links
Integral
Stellar Chemistry, The Universe And All Within It
Understanding Time and Space



Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News


New Clue To Tiniest Particles
Adelaide, Australia (SPX) Sep 06, 2006
Particle physicists around the world will be designing their next generation of billion-dollar experiments following new findings from a University of Adelaide-led research team. The Holy Grail of the world's particle physicists is to discover and describe new particles that make up the Universe's tiniest building blocks.







  • Moscow Mayor Says Winter Energy Deficit Could Reach 20 Percent
  • Fresh Declines For Oil Prices As Iran Fears Recede
  • Schwarzenegger Ready To Sign Bill Limiting Greenhouse Gas Emissions
  • Schwarzenegger Caps Greenhouse-Gas Emissions In California

  • Australia Could Export Uranium To China Within Months
  • Russia To Sell Nuke Fuel To South Africa
  • Understanding Reactor Security Fears In The 21st Century
  • Iran Hopes Russia Will Be Main Bidder In Two New NPP Projects

  • NASA Experiment Finds Possible Trigger For Radio-Busting Bubbles
  • California's Model Skies
  • ESA Picks SSTL To Develop Atmospheric CO2 Detector
  • Faster Atmospheric Warming In Subtropics Pushes Jet Streams Toward Poles

  • Large-Scale Farming Now Causes Substantial Forest Loss in Amazon
  • The Subtleties Of Tropical Forest Demise
  • NASA Satellites Can See How Climate Change Affects Forests
  • Papua Logging Industry Riddled With Corruption, Rights Abuses: Report

  • China Rejects Claims Of GM Rice Entering EU Foods
  • GM Chinese Rice Maybe Contaminating European Food
  • French Police Arrest Three As Hundreds Try To Destroy GM Crops
  • Japanese Sushi Infatuation Straining Atlantic Tuna Stocks

  • Real-Time Traffic Routing From The Comfort Of Your Car
  • Real-Time Traffic Routing From The Comfort Of Your Car
  • British Police Force To Introduce Greener Cars
  • Two New Segway Models Offered

  • US Sanctions On Russia Could Hurt Boeing
  • Boeing Puts Aircraft Market At 2.6 Trillion Dollars
  • Innovative Solutions Make Transportation Systems Safer Secure and Efficient
  • Joint Strike Fighter Is Not Flawed Finds Australian Government

  • Could NASA Get To Pluto Faster? Space Expert Says Yes - By Thinking Nuclear
  • NASA plans to send new robot to Jupiter
  • Los Alamos Hopes To Lead New Era Of Nuclear Space Tranportion With Jovian Mission
  • Boeing Selects Leader for Nuclear Space Systems Program

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2006 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA PortalReports are copyright European Space Agency. All NASA sourced material is public domain. Additionalcopyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement