NASA ESA Hubble Image: Galactic Collision

Astronomical pictures sometimes deceive us with tricks of perspective. 

Right in the center of this image, two spiral galaxies appear to be suffering a spectacular collision, with a host of stars appearing to flee the scene of the crash in a chaotic stampede.

However, this is just a trick of perspective.

It is true that two spiral galaxies are colliding, but they are millions of light-years away, far beyond the cloud of blue and red stars that appear to be near the merging spiral.

This sprinkling of stars is actually an isolated, irregular dwarf galaxy named ESO 489-056.

The dwarf galaxy is actually much more distant than many bright stars in the foreground of the image, which are located much closer to us, in the Milky Way.

ESO 489-056 is located 16 million light-years from Earth in the constellation of Canis Major (The Greater Dog), in our local Universe.

It is composed of a few billion red and blue stars—a very small number when compared to galaxies like the Milky Way, which is estimated to contain around 200 to 400 billion stars, or the Andromeda Galaxy, which contains a mind-boggling one trillion.

When Galaxies Collide: Linked Arms

The two galaxies seen here, NGC 6050 and IC 1179, are located about 450 million light-years away in the constellation Hercules.

The spiral bodies are seen crashing together, with an enormous eddy of stars seeming to form between their conjoined arms.

This object is part of the Hercules Galaxy Cluster, itself located within the Great Wall of superclusters, the largest known structure in the universe.

Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and K. Noll (STScI)

Spiral Arms Point to Possible Planets in a Star's Dusty Disk

Two spiral arms emerge from the gas-rich disk around SAO 206462, a young star in the constellation Lupus. 

This image, acquired by the Subaru Telescope and its HiCIAO instrument, is the first to show spiral arms in a circumstellar disk. 

The disk itself is some 14 billion miles across, or about twice the size of Pluto's orbit in our own solar system. (Credit: NAOJ/Subaru)

A new image of the disk of gas and dust around a sun-like star is the first to show spiral-arm-like structures.

These features may provide clues to the presence of embedded but as-yet-unseen planets.

"Detailed computer simulations have shown us that the gravitational pull of a planet inside a circumstellar disk can perturb gas and dust, creating spiral arms.

Now, for the first time, we're seeing these dynamical features," said Carol Grady, an astronomer with Eureka Scientific, Inc., who is based at NASA's Goddard Space Flight Center in Greenbelt, Md. Grady revealed the images at the Signposts of Planets meeting hosted this week at the center.

Grady's research is part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS), a five-year-long near-infrared study of young stars and their surrounding dust disks using the Subaru Telescope atop Mauna Kea in Hawaii.

The international consortium of researchers now includes more than 100 scientists at 25 institutions.

"What we're finding is that once these systems reach ages of a few million years, their disks begin to show a wealth of structure - rings, divots, gaps and now spiral features," said John Wisniewski, a collaborator at the University of Washington in Seattle.

"Many of these structures could be caused by planets within the disks."

The newly imaged disk surrounds SAO 206462, an 8.7-magnitude star located about 456 light-years away in the constellation Lupus. Astronomers estimate that the system is only about 9 million years old.

The gas-rich disk spans some 14 billion miles, which is more than twice the size of Pluto's orbit in our own solar system.

The Subaru near-infrared image reveals a pair of spiral features arcing along the outer disk. Theoretical models show that a single embedded planet may produce a spiral arm on each side of a disk.

The structures around SAO 206462 do not form a matched pair, suggesting the presence of two unseen worlds, one for each arm.

However, the research team cautions that processes unrelated to planets may give rise to these structures.

The view was made possible by the High Contrast Instrument for the Subaru Next Generation Adaptive Optics, or (HiCIAO, pronounced "HI-chow"), which is designed to block out harsh direct starlight.

NASA - Spiral Extraordinaire

Scientists have yet to discover what caused the strange spiral structure. Nor do they know why it glows.

The glow may be caused by light reflected from nearby stars. As for the spiral itself, current supposition is that this is the result of a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected.

Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The above image was taken in near-infrared light by the Hubble Space Telescope.

Image Credit: NASA, ESA, Hubble, R. Sahai (JPL)

NASA Charles Messier's catalogue spiral nebula NGC 5194

This NASA image obtained shows the 51st entry in Charles Messier's catalogue, perhaps the original spiral nebula, also catalogued as NGC 5194.

Over 60,000 light-years across, M51's spiral arms and dust lanes clearly sweep in front of its companion galaxy, NGC 5195.

Image data from the Hubble's Advanced Camera for Surveys was reprocessed, which sharpened details and enhanced colour and contrast in otherwise faint areas, bringing out dust lanes and extended streams that cross the small companion, along with features in the surroundings and core of M51 itself

Picture: AFP/GETTY / HUBBLE HERITAGE TEAM