Astronomers have spotted a rare, complex cosmic collision of four galaxy clusters. A spectacular composite image from NASA's Chandra X-Ray Observatory and Hubble Space Telescope revealed the pileup—and its likely source.

To learn about other recent astronomical discoveries, visit the Science Bulletins website.

To understand how the modern Universe came to be, astronomers turn to computer models, programs that follow the physical laws of the Universe. Computer models can be run backward to reconstruct the past or forward to predict the future. A team of researchers from the Institute for Computational Cosmology at Durham University in the UK recently used computer models to simulate how the Universe’s big galaxies have changed over billions of years.

Their starting point was 500 million years after the Big Bang. At this time, big star-forming galaxies built up from gas that was clumping along filaments of dark matter, an invisible substance that pervades the Universe. The galaxies coalesced at dense points of dark matter where its gravity was strongly attractive. The team let the dark matter and the galaxies in the model evolve to the present day. The computational effort required both the Millenium Simulation, a simulation of how structures grow in dark matter, and a computer model that mimics how normal matter, such as gas, behaves.

The results showed that galaxies were at their peak of star formation somewhere between 2 billion and 3 billion years after the Big Bang, and have tapered off in modern times. Today, galaxies are far less active because most of their gas is already locked up in stars. Now, researchers can compare the computer model’s results with modern telescope maps of the Universe, such as those from VISTA, a new sky survey telescope at Chile’s Paranal Observatory. These comparisons can help the team gauge the accuracy of their galactic time machine.

To learn about other recent astronomical discoveries, visit the Science Bulletins website.

Scientists have announced that they have tracked an asteroid from space all the way to its impact on Earth, a first for astronomy. Space rocks are called asteroids when they are in orbit and meteorites when they land on Earth. Scientists who collect meteorites usually do not know the specific asteroid that they came from—until now.

In early October 2008, numerous Earth-based telescopes spotted the asteroid 2008 TC3 careening toward Earth. Its landing spot was calculated to be the Nubian Desert of northern Sudan. Deserts are ideal places to collect meteorites because the space rocks are easily spotted on a monochromatic surface without vegetation. But it was expected that this small asteroid would largely vaporize because of friction from air molecules upon entry.

Astronomer Peter Jenniskens of the SETI Institute in Mountain View, California, took the chance that some of the asteroid survived. He organized a search party with students and staff from the University of Khartoum, and they successfully gathered 4 kilograms of fresh black meteorite fragments from the landing site. “For the first time we can dot the line between the meteorite in our hands and the asteroid that astronomers saw in space,” said Jenniskens in a NASA press conference. The discovery has improved astronomers’ understanding of asteroids, information that may be critical if a larger, more destructive asteroid hits Earth in the future.

To learn about other recent astronomical discoveries, visit the Science Bulletins website.