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Black Holes Grow Fat by Eating Stars

By David Reneke

News from the space and astronomy communities around the world.

Black holes are objects in space so dense that not even light can escape their gravity, although powerful jets of light and energy can be emitted from a black hole’s vicinity as gas and stars are sucked into it.

Small black holes result from the collapse of individual stars, but the centres of most galaxies – including our own Milky Way – are occupied by supermassive black holes with masses between one million and ten billion times that of our Sun.

New research being carried out at the University of Utah and the Harvard-Smithsonian Centre for Astrophysics (CfA) shows that supermassive black holes can grow bigger by ripping apart double star systems and swallowing one of the stars. Tidal forces capture one star and eject the other. The captured star orbits around the black hole, later becoming fodder for the galactic monster.

“Black holes are very efficient eating machines,” said Scott Kenyon of the CfA. “They can double their mass in less than a billion years. That may seem long by human standards, but over the history of the galaxy it’s pretty fast.”

As many as half of all stars are in binary pairs. Crunching the numbers, the rate of observed binary encounters with our galaxy’s supermassive black hole would mean that most of the mass of the black hole came from binary stars. The same seems to apply in other galaxies as well.

When researchers considered the number of stars near the Milky Way’s centre, their speed and the odds they will encounter the supermassive black hole, they estimated that one binary star will be torn apart every 1000 years by the black hole’s gravity.

During the past 10 billion years that would mean the Milky Way’s supermassive black hole ate 10 million solar masses, more than enough to account for the hole’s actual size of four million solar masses.

Designing the Interplanetary Web
Reliable internet access on the Moon, near Mars or for astronauts on a space station? How about controlling a planetary rover from a spacecraft in deep space? These are just some of the pioneering technologies that the European Space Agency (ESA) is working on for future exploration missions.

We need to keep in mind that we’re living in yesterday’s future. Communication is the byword for the 21st century. As we develop into a spacefaring society we’ll all need to send data back home, and the complexity of sharing that information across space is set to grow.

In the future, rovers on Mars or inhabited bases on the Moon will be supported by orbiting satellite fleets providing data relay and navigation services. Astronauts hundreds of millions of kilometres from Earth will need to link up with other astronauts, control centres and sophisticated systems on their vessels.

All of these activities will need to be interconnected, networked and managed. “We are researching how today’s technical standards for devices like mobile phones, laptops and portable computers can be applied to a new generation of networked space hardware,” says Nestor Peccia at ESA’s Operations Centre in Darmstadt, Germany.

Since 1982, experts from ESA, NASA and other major space organisations and industry have met periodically to develop open data communication standards as part of the Consultative Committee for Space Data Systems.

In the future, inter-satellite communication requirements are predicted to grow, and spacecraft should be capable of establishing powerful radio links with each other – even while orbiting Mars at thousands of kilometres per hour.

“Setting technical standards and communication system architecture is going to be absolutely vital for ensuring highly sophisticated programs like a manned Mars mission or outer planet exploration will work as planned when that time comes,” says Nestor.

For now, orbital internet is limited to the International Space Station. Since January 2010 its astronauts have had access to so-called Crew Support LAN, which uses satellites to provide a brisk, reliable internet connection. Prior this, going online in orbit was a hassle. E-mails, tweets and other online exchanges had to be relayed through a colleague on Earth, which was hardly ideal – especially for intimate communications.

The current system has undoubtedly improved the quality of life on the International Space Station, helping to ease the sense of isolation. It is a far cry from interplanetary social networking, but it is a start.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at