Australasian Science Magazine

By David Reneke

The Hubble has found Kuiper Belt targets for the New Horizons program, and monster galaxies are gaining weight by cannibalising neighbours.

The Hubble Space Telescope has uncovered three Kuiper Belt objects (KBOs) that NASA’s New Horizons spacecraft could potentially visit after it flies by Pluto in July 2015.The New Horizons spacecraft, launched in 2006, is the first mission in NASA’s New Frontiers Program.

The Kuiper Belt is a vast rim of primordial debris encircling our solar system. KBOs belong to a unique class of solar system objects that has never been visited by spacecraft.

So why go there? Well, astronomers believe these mini worlds could contain clues to the origin of our solar system, including the biomarkers that eventually kickstarted life here.

The KBOs Hubble found are each about 10 times larger than typical comets, but only about 1–2% of the size of Pluto. Unlike asteroids, KBOs have not been heated by the Sun and are thought to represent a pristine, well-preserved deep freeze sample of what the outer solar system was like following its birth 4.6 billion years ago. The KBOs found in the Hubble data are thought to be the building blocks of dwarf planets such as Pluto.

The New Horizons team started to look for suitable KBOs in 2011 using some of the largest ground-based telescopes on Earth. Several dozen KBOs were initially identified, but most were beyond New Horizon’s boundaries.

Eventually the Hubble Space Telescope came to the rescue with new reachable targets identified. “There was a huge sigh of relief when we found suitable KBO,” said New Horizons science team member John Spencer.

Three main KBOs were identified, each a whopping 1.5 billion km beyond Pluto. Two of the KBOs are estimated to be as large as 55 km across, and the third is perhaps as small as 25 km.

Monster Galaxies Gain Weight by Cannibalising Neighbours

Massive galaxies in the universe have stopped making their own stars and are instead snacking on nearby galaxies, according to research by Australian astronomers. They looked at more than 22,000 galaxies and found that while smaller galaxies are very efficient at creating stars from gas, the most massive galaxies are much less efficient at star formation, producing hardly any new stars themselves, and instead grow by eating other galaxies.

Dr Aaron Robotham at The University of Western Australia node of the International Centre for Radio Astronomy Research said smaller “dwarf” galaxies were being eaten by their larger counterparts. “All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars,” he said. “Then every now and then they get completely cannibalised by some much larger galaxy.”

Our own Milky Way is expected to continue growing, mainly by eating smaller galaxies than by collecting gas. The Milky Way hasn’t merged with another large galaxy for a long time but remnants of all the old galaxies we’ve consumed are still evident. We’re also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years.

But Robotham said the Milky Way is eventually going to get its just desserts when it merges with the nearby Andromeda Galaxy in about five billion years. “Technically, Andromeda will eat us because it’s the more massive one,” he said.

As galaxies grow, their gravitational field increases and they reel in their neighbours with ease. Ultimately, gravity is expected to cause all the galaxies in bound groups and clusters like ours to merge into a few supergiant galaxies, although we will have to wait many billions of years before that happens.

“If you waited a really, really, really long time that would eventually happen, but by really long I mean many times the age of the universe so far,” Robotham said.

Almost all of the data for the research was collected with the Anglo-Australian Telescope as part of the Galaxy And Mass Assembly (GAMA) survey over a 7-year period.

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 www.davidreneke.com