SLAC’s New KIPAC Tool Gives Scientists a Closer Look at Merging Galaxies

Hubble Space Telescope image of two galaxies merging. This system is known as the “Antennae Galaxies.” (Image courtesy Hubble Space Telescope)

Scientists at SLAC’s Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) have created sophisticated computer simulations that show galaxy mergers in much more detail than ever before.

On large cosmic scales, galaxies are the fundamental “molecular” units that occupy much of space.

Understanding how they gravitationally interact is an important part of astrophysical research, since they can help explain star formation and other phenomena.

Central black holes in some galaxies, for example, create huge jets of energy, a mysterious activity that intrigues researchers.

Mergers between galaxies are rare. Based on its relatively undisturbed structure, we can estimate that our own Milky Way galaxy has not been part of any major mergers within the last 10 billion years.

When they do happen, they can produce some of the most awe-inspiring images from space. Such events may completely change the size and shape of galaxies, disrupting spiral arms and funneling stars into central bulges.

Individual stars are so far apart from each other, however, that an actual collision between two of them is extremely unlikely.

It is difficult to completely resolve the details of two interacting galaxies simply by observing them.

So scientists devise computer simulations of millions of galaxies evolving through the history of the universe, hoping to see mergers in process.

Impossible to manage by hand, the immense amount of detail involved in these simulations requires special tools for tracking clusters of galactic matter over time.

However, current analysis tools can’t differentiate the uniquely individual parts of galaxies during a merger, so the most interesting fine details are lost as the two galaxies become one.

To solve this problem, KIPAC graduate student Peter Behroozi, along with Professor Risa Wechsler and recent KIPAC alumna Heidi Wu, developed a new computational algorithm that uses both position and velocity information to distinguish galaxies in simulations.

The algorithm’s formal name is Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement (ROCKSTAR - Pdf).

In essence, the program accounts for the speed, location and direction of the galactic elements. The result is a highly detailed picture of galaxy formation and disruption.

By extension, the algorithm’s measurement of galactic motions will also contribute to the larger study of the mass and energy content of the universe.

This work is based in part on a paper submitted to The Astrophysical Journal, online now on arXiv, and on an article by Peter Behroozi and Jack Singal for the KIPAC “Tidbits” newsletter.

NASA: First Monarch Butterflies Emerge in the ISS

The first-ever Monarch butterflies in space have taken flight on the International Space Station to the delight of astronauts aboard.

Space station commander Jeff Williams, of NASA, beamed video of the first of several Monarch butterflies fluttered its gossamer wings in weightlessness last week, just after the insect emerged from its cocoon and began floating around their enclosure.

"It is beautiful," Williams radioed Mission Control. "It's always beautiful to see a little bit of Earth up here."

The video showed one adult Monarch butterfly floating gently in microgravity as it opened and closed its wings to dry them. "Congratulations to the experiment team," Williams said.

"They are very proud parents," Mission Control radioed back. "Glad you finally got the video. It's a pretty awesome site."

The Monarch butterflies are the first ever sent to space. They began emerging just days after several Painted Lady butterflies began emerging from their own cocoons in a separate enclosure.

The Monarch and Painted Lady butterflies arrived at the station as catepillars last month on the space shuttle Atlantis as part of an educational experiment. And while butterfly larvae have been sent to space before, the colorful insects on the space station now are the first to successfully go through all phases of their development — from larva to pupa to adult butterfly — in orbit.

More than 170,000 students between kindergarten and 12th grade and 2,800 teachers are following the experiment on Earth, where they are comparing the space butterflies' lifecycle with that of similar insects on the ground. The butterflies also have their own Twitter page "ButterflySpace" where status updates of their space mission appear.

At least one difference between space Monarch butterflies and their terrestrial counterparts has already been revealed. On Earth, the wings of a newly-emerged Monarch butterfly can take anywhere between three and five minutes to dry. But aboard the space station, it took about 15 minutes.

The Monarch and Painted Butterflies were delivered to the space station inside a habitat known as the Commercial Generic Bioprocessing Apparatus Science Insert – 03. It was built by BioServe Space Technologies at the University of Colorado at Boulder.