RSSArchive for March, 2010

Black holes light up as they gain weight

Examples of strongly interacting/merging galaxies

Examples of strongly interacting/merging galaxies containing a heavily obscured growing supermassive black hole nearby (top panels) and in the early Universe (bottom panels), as observed by the Hubble Space Telescope.

Giant black holes in the centres of galaxies grow mainly as a result of intergalactic collisions, according to results presented by a group of astronomers led by Dr Ezequiel Treister from the University of Hawaii, published in the March 25th issue of the international journal Science.

As gas clouds in galaxies are sucked into the central black hole, they emit vast amounts of radiation, giving rise to objects that astronomers call quasars.

“We find that these growing black holes are originally hidden by large amounts of dust”, Treister said, “but after 10-100 million years this dust is blown out by the strong radiation pressure, leaving a naked quasar, [which] is visible in optical wavelengths and keeps shining for another 100 million years”.

For this study, the group combined data obtained with the Hubble, Chandra and Spitzer space observatories to identify a large number of obscured, dust enshrouded quasars at very large distances, up to 11 billion light-years away when the Universe was still in its infancy.

“For many years, astronomers believed that these sources were very rare. Now we are seeing them everywhere!” Treister added.

Because most of the emission from these obscured quasars is hidden, astronomers looked at infrared wavelengths, for signs of very hot dust, and in X-rays, which are less affected by obscuration. The investigators discovered that the number of obscured quasars relative to the unobscured ones was significantly larger in the early Universe than it is now.

Artist's view of the quasar stages after a major galaxy merger. Graphcy by Karen Teramura.

Artist's view of the quasar stages after a major galaxy merger. Graphcy by Karen Teramura.

“We knew theoretically that the mergers of massive gas-rich galaxies were more frequent in the past; these observations fit very nicely within this scenario”, added Prof. Priyamvada Natarajan of Yale University, the second author and theorist on the team.

“We knew that this is definitely the case for nearby galaxies”, said Prof. David Sanders from the University of Hawaii and participant in this investigation, “but this result shows that this happens across the Universe”.

Researchers further analysed images of these distant galaxies taken by the Hubble Space Telescope, using the new Wide Field Camera 3 installed 10 months ago during the last servicing mission. These images revealed obvious signatures of interactions and mergers, thus confirming the hypothesis of this group. Finally, using a simple theoretical prescription, the authors estimated that it takes about 100 million years for radiation from the growing black hole to wipe out the surrounding dust and gas and reveal the naked quasar.

Major galaxy mergers are important to trigger star formation episodes and modify galaxy shapes and sizes. “This work confirms that mergers are also critical for the growth of the nuclear giant black hole”, said Natarajan. Mergers are therefore essential for the evolution of a galaxy and also cause their central black hole to gain weight during both the obscured and unobscured phases.

Martian “blueberries” intrigue rover scientists

Artist's impression of the Mars rover Opportunity

Artist's impression of the Mars rover Opportunity

Weird coatings on rocks beside a young Martian crater remain puzzling after a preliminary look at data from examination of the site by NASA’s Opportunity rover.

The rover spent six weeks investigating the crater called “Concepcion” before resuming its long journey this month. The crater is about 10 metres (33 feet) in diameter. Dark rays extending from it, as seen from orbit, flagged it in advance as a target of interest because the rays suggest the crater is young.

An image from orbit showing Opportunity beside Concepcion

An image from orbit showing Opportunity (black dot in the 1 o'clock position) beside crater Concepcion.

The rocks ejected outward from the impact that dug Concepcion are chunks of the same type of bedrock Opportunity has seen at hundreds of locations since landing in January 2004: soft, sulphate-rich sandstone holding harder peppercorn-size dark spheres like berries in a muffin. The little spheres, rich in iron, gained the nickname “blueberries.”

“It was clear from the images that Opportunity took on the approach to Concepcion that there was strange stuff on lots of the rocks near the crater,” said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for Opportunity and its twin rover, Spirit. “There’s dark, greyish material coating faces of the rocks and filling fractures in them. At least part of it is composed of blueberries jammed together as close as you could pack them. We’ve never seen anything like this before.”

Opportunity used tools on its robotic arm to examine this unusual material on a rock called “Chocolate Hills.” In some places, the layer of closely packed spheres lies between thinner, smoother layers. “It looks like a blueberry sandwich,” said Matt Golombek, a rover science-team member at NASA’s Jet Propulsion Laboratory, Pasadena, California.

An image of the strange Martian rock coating dubbed "blueberries".

An image of the strange Martian rock coating dubbed "blueberries".

Initial analysis of the coating’s composition does not show any obvious component from whatever space rock hit Mars to dig the crater, but that is not a surprise, Golombek said. “The impact is so fast, most of the impactor vaporizes,” he said. “Thin films of melt get thrown out, but typically the composition of the melt is the stuff that the impactor hit, rather than the impactor material.”

The composition Opportunity found for the dark coating material fits at least two hypotheses being evaluated, and possibly others. One is that the material resulted from partial melting of blueberry-containing sandstone from the energy of the impact. Another is that it formed from filling of fractures in this type of rock before the impact occurred.

“It’s possible that when you melt this rock, the sandstone melts before the blueberries do, leaving intact blueberries as part of a melt layer,” Squyres said. “As an alternative, we know that this type of rock has fractures and that the sandstone can dissolve. Long ago, water flowing through fractures could have dissolved the sandstone and liberated blueberries that fell down into the fracture and packed together. In this hypothesis, the impact that excavated the crater did not play a role in forming this material, but split rocks along fractures so the material is exposed on the exterior like a coating.”

Golombek said, “One consideration that jumps out is that we’ve been driving around this part of Mars for six years and never seen this stuff before, then we get to this young crater and it’s coating rocks all around the crater. Sure looks like there’s a connection, but it could just be a coincidence.”

The observation that the rocks thrown from the crater have not yet eroded away much is evidence that the crater is young, confirming the suggestion from the dark rays. Squyres said, “We’re not ready to attach a number to it, but this is really young. It is the youngest crater we’ve ever seen with Opportunity and probably the youngest either rover has seen.”

One question Opportunity’s visit did answer was about the dark rays: “We wondered before getting to Concepcion why the rays are dark,” Golombek said. “We found out that the rays are areas with blocks of light-toned sandstone ejected from the crater. They look dark from orbit because of the shadows that the blocks are casting when the orbital images are taken in mid-afternoon.”

Since departing Concepcion on March 9, Opportunity has driven 614 metres (2,014 feet) farther along the route to its long-term destination at Endeavour Crater, about 19 kilometres (12 miles) in diameter and still at a drive distance of more than 12 kilometres (7 miles).

Squyres said, “We’re on the road again. We have a healthy rover and we have enough power for substantial drives. We want to get to Endeavour with a healthy rover. It takes a compelling target for us to stop and study. And Concepcion was a compelling target.”

Shuttle launch video

This is a video of the last planned night launch of a space shuttle. Endeavour launched on February 8, 2010 on a mission to the International Space Station, carrying the Tranquility module and the Cupola, an observation post with windows that enable Station crewmembers to see what’s happening outside.

Europe’s proposed tourist spaceplane

Watch this beautiful video of EADS Astrium’s proposed spaceplane.

Perth’s radio astronomy centre

A new astronomy centre, the International Centre for Radio Astronomy Research, has been established in Perth, Australia, to support and boost Australia’s 21st century radio astronomy research efforts.

Australia is currently building ASKAP, the Australian Square Kilometre Array Pathfinder, which will be a network of 36 radio dish antennae. ASKAP will become one of the world’s foremost astronomy observatories, and for some types of research programs, it will be the best in the world.

As the name suggests, ASKAP is intended to be the forerunner to the Square Kilometre Array, a radio telescope system that will be the world’s largest observatory (in terms of geographical spread). Comprising hundreds of antennae spread over thousands of square kilometres, the total area of all the dishes and other antennae combined will add up to one square kilometre, hence the name.

Australia and southern Africa are vying for the rights to host the facility. A decision is expected sometime within the next couple of years.

Video courtesy of ICRAR.

ASKAP, Australia’s new “Dish” radio telescope

Watch this fabulous animation of Australia’s next-generation radio telescope system, the Australian Square Kilometre Array Pathfinder, or ASKAP.

ASKAP is being built in a remote corner of Western Australia, where the environment is “radio quiet”, ie. there is little radio interference from man-made sources.

When operational in 2013, it will be one of the world’s best radio telescope systems. In fact, for many types of astronomy, it will be the best radio telescope. It will have electronic “fish eye” technology that enables it to see huge areas of the sky at once, which means that it will be able to conduct whole-sky surveys with impressive speed. This efficiency means astronomers will be able to achieve in a matter of months or years what would have taken decades to do before.

The animation was produced by the Swinburne Centre for Astrophysics and Supercomputing.

The Whitsunday Islands

The Whitsunday Islands, seen from orbit

The Whitsunday Islands, seen from orbit

The Whitsunday Islands are a collection of 74 islands sandwiched between the Australian mainland and the outer atolls of the Great Barrier Reef. Most of the island chain is protected national park within the Great Barrier Reef Marine Park, though a number of resorts and camping areas exist on the islands.

This photo-like image of the core of the Whitsunday Islands was acquired by the Enhanced Thematic Mapper Plus (ETM+) instrument on NASA’s Landsat 7 satellite. The entire chain of islands and the outer reef section of the Great Barrier Reef appear in the large image.

The scene is dominated by the largest island and namesake of the chain. Deep green forest covers most of Whitsunday Island, which is outlined by brilliant white sand beaches, the largest and most dramatic being Whitehaven Beach at the south-eastern end of the island.

On Hamilton Island, the strong linear feature at the southern end shows where a jet-accessible runway was added to allow airlines from major Australian cities to fly directly to the islands. The swirls of pale blue around the islands show a mix of sandy bottom waters and shallow, fringing coral reefs. The green land in the southwestern corner of the image is a small section of Conway Ranges National Park, on the shoreline of mainland Queensland.

The island’s name comes from the journals of Captain James Cook who sailed through the area in early June 1770. He christened the largest island in honour of the date he arrived, Whit Sunday, the seventh Sunday after Easter. (The name stuck even after it was discovered that a date error meant it was actually Monday when Cook’s ship, the Endeavour, arrived.)

The islands, parks, and resorts of the Whitsunday Islands are among the most popular tourist destinations for visitors to the Great Barrier Reef; boat trips from the mainland and Hamilton Island take visitors to the Outer Reef and to destinations in and around the islands. The waters between the mainland and these islands was used during the Second World War as a shelter from storms (and detection by Japanese forces) for the US Navy prior to the Battle of the Coral Sea.

NASA Earth Observatory image created by Jesse Allen, using Landsat data provided by the United States Geological Survey. Caption adapted from information issued by Jesse Allen.

Astronauts’ “out of this world” view of Earth

The view looking out of the windows of the International Space Station's new "cupola" viewing module.

The view looking out of the windows of the International Space Station's new "cupola" viewing module.

Astronauts onboard the International Space Station (ISS) have a new view of Earth after the space shuttle Endeavour delivered the Tranquility module to the station.

Measuring 5m wide by 7.5m long, Tranquility holds some of the station’s environmental control equipment, such as the system that cleans carbon dioxide from the air, and it also provides living space for exercise equipment and a bathroom.

Tranquility also comes with a cupola, a dome-shaped viewing port made up of seven windows.

Shortly after the shutters were removed from the cupola windows on February 17, Japanese astronaut Soichi Noguchi took the top photo while looking out from the new cupola. The Sahara Desert is visible through the windows. On February 19, an astronaut captured the photo below—looking into the cupola at STS-130 mission commander George Zamka, who was visiting the Space Station’s “new wing” while the shuttle was still docked to the station.

“The cupola is intended to enhance situational awareness for ISS operations like spacecraft docking, EVAs [Extra Vehicular Activities, spacewalks], and robotic operations,” says William Stefanov of the Image Science and Analysis Laboratory at Johnson Space Centre, a lab set up to help astronauts take pictures of Earth that will be of greatest value to scientists and the public.

Many of those activities require astronauts to control tools and machines remotely while watching their progress on a monitor. (Imagine trying to mow your lawn with a remote controlled lawnmower and a fixed video camera.)

Astronaut George Zamka can be seen through one of the windows of the cupola.

Astronaut George Zamka can be seen through one of the windows of the cupola.

But while the view out of Tranquility was primarily designed to give astronauts a way to see the outside of the station itself, it also provides a stunning panoramic view of Earth and space.

“There is no intention to focus astronaut photography of the Earth through the cupola, but it will almost certainly be used for that purpose by crewmembers,” says Stefanov.

In an essay published on the Earth Observatory in October 2003, Astronaut Ed Lu described the experience of seeing the Earth from the International Space Station. “When I look out a window that faces straight down, it is actually pretty hard to see the horizon—you need to get your face very close to the window. So what you see out a window like that is a moving patch of ground (or water),” he wrote. “When looking out a sideward facing window, you can see the horizon of the Earth against the black background of space.”

The cupola will allow astronauts the luxury of both views at once.

NASA photographs ISS022-E-066972 and ISS022-E-068726 courtesy Johnson Space Centre. Caption adapted from information issued by Holli Riebeek.

Final shuttle fuel tank spliced together

The fuel tank for the final space shuttle mission

The fuel tank for the final space shuttle mission

The space shuttle programme’s final flight tank—designated External Tank-138—has completed a critical production milestone at the NASA Michoud Assembly Facility.

Lockheed Martin builds the External Tanks in New Orleans where its engineers and technicians mechanically spliced ET-138’s liquid oxygen (LO2)/intertank to the liquid hydrogen (LH2) tank, thus producing “a whole tank” for the first time in the production process.

The work is performed in Cell A in the 20-story-tall Vertical Assembly Building, and is the only time during production that the tank stands upright. Workers also completed foam “closeouts” on the LH2 to intertank flange.

The fuel tank for the final space shuttle mission

Another view of the fuel tank

An External Tank is actually three components in one. The 16.6m-tall bullet-shaped LO2 tank sits at the top. The 7m-long intertank separates the LO2 tank and the LH2 tank and does not hold fuel. Unpressurised, the intertank serves as the forward attachment point for the Solid Rocket Boosters. The bottom vessel is the 29.5m-tall LH2 tank. The LO2 tank and intertank are already spliced together when they enter Cell A.

Lockheed Martin employees loaded the tanks into the cell and completed the splicing and laydown of the tank in a record 40 days. The prior eight tanks averaged 60 days in Cell A.

ET-138 now proceeds to the Final Assembly area for more processing and is scheduled for completion June 29. When ET-138 is delivered to NASA, it will be 15 stories tall (47m), nearly 8.5m in diameter, and weigh 26.3 tonnes empty. When filled with 2,021,000 litres of propellant on the launch pad, the tank will weigh nearly 771 tonnes.

ET-138 is scheduled to launch with Space Shuttle Discovery (STS-133) on September 16—the final shuttle launch of the 29-year programme. ET-138 will help propel Discovery to orbit and then separate from the shuttle 8.5 minutes post-launch after Main Engine Cut-off or MECO.

ET-138 will be the 134th flight tank that Lockheed Martin has constructed for the shuttle programme.

Adapted from information issued by Lockheed Martin.

Smallest known star duo confirmed

Artist's impression of the binary star system known as HM Cancri

About 1,600 light-years away, in a binary star system known as HM Cancri, two dense white dwarf stars orbit each other once every 5.4 minutes, based on data from the Keck Observatory. This artist's rendition shows the dance of these dead stars and the resulting gravitational waves (which would actually be invisible).

Astronomers have identified the smallest known binary star system to date. Called HM Cancri, its consists of two dead stars that revolve around each other in 5.4 minutes, by far the shortest known orbital period of any pair of stars.

The team, led by Gijs Roelofs of the Harvard-Smithsonian Center of Astrophysics, used the 10-meter Keck I telescope in Hawaii and its Low Resolution Imaging Spectrograph to study the velocity changes in the spectral lines in the light coming from HM Cancri.

They saw that as the stars orbited each other, the system’s spectral lines shifted periodically from blue to red and back, in accordance with the Doppler effect. With that velocity information, the astronomers were able to confirm the binary’s 5.4-minute period.

“When the first data from the Keck telescope arrived, and our quick analysis showed the periodic shift of the spectral lines, we knew that we had succeeded. More than ten years after its discovery, we finally had deciphered the nature of HM Cancri,” said Arne Rau of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who led the observations at Keck.

Astronomers proposed several years ago that HM Cancri was an interacting binary consisting of two dead stars and that the 5.4 minute period observed was indeed the orbital period.

The team had been trying to make precise velocity measurements to confirm the period since 2005.

X-ray evidence

HM Cancri was discovered in 1999 as a weak X-ray source in data from the German ROSAT satellite. It comprises two white dwarfs, burnt-out cinders of stars that were once similar to the Sun and contain a highly condensed form of helium, carbon and oxygen. In 2001, the X-ray, and also optical, data suggested that the two stars orbited each other in 5.4 minutes.

Another artist's conception of HM Cancri.

Another artist's conception of HM Cancri. One star is feeding the other.

But the information suggested that the binary system was roughly eight times the diameter of the Earth—equivalent to a quarter of the distance between the Earth and the Moon—or smaller. Astronomers were reluctant to accept this physical description without additional evidence. But at a distance of 16,000 light years from Earth, the binary system shines only one millionth as bright as the faintest stars visible to the naked eye, making it very hard to study. To determine with certainty the period of such a system, astronomers needed to use world’s largest telescopes to collect the additional evidence.

“This type of observation is really at the limit of what is currently possible. Not only does one need the biggest telescopes in the world, but they also have to be equipped with the best instruments available,” said team member Paul Groot of the Radboud University Nijmegen in the Netherlands.

As a result of the successful observations with Keck, astronomers now have a new cosmic laboratory to study the evolution of stars as well as general relativity.

“We know the system must have come from two normal stars that somehow spiralled together in two earlier episodes of mass transfer, but the physics of this process is very poorly understood,” said Gijs Nelemans of the Radboud University who was also part of the team.

He added that the system must be one of the most copious emitters of gravitational waves. “We hope to detect these distortions of space-time directly with the future LISA satellite. HM Cancri will now be a cornerstone system for the mission,” he said.

Adapted from information issued by Keck Observatory / NASA / Tod Strohmayer (GSFC) / Dana Berry (Chandra X-Ray Observatory) / Rob Hynes and Paul Groot, Radboud University.