Galactic Fireworks

January 2, 2005
Gemini North GMOS image of the 'Fireworks Galaxy' NGC 6946 in the Constellation of Cepheus

Astronomers at Gemini Observatory are ushering in the New Year with a striking image that dazzles the eye with stellar pyrotechnics.
The image of the face-on spiral galaxy NGC 6946 is ablaze with a colourful galactic fireworks display fuelled by the births and deaths of multitudes of brilliant, massive stars. Astronomers suspect that massive stars have been ending their lives in supernova explosions throughout NGC 6946 in rapid-fire fashion for tens of millions of years.

Image: Gemini North GMOS image of the 'Fireworks Galaxy' NGC 6946 in the Constellation of Cepheus. Credit: Gemini Observatory

"If you could make a time-lapse movie that compressed millions of years into seconds, this galaxy would resemble a sparkler," said Dr Rachel Johnson, UK Gemini Spokesperson from the University of Oxford. "New stars would flare into view as old stars expired in huge explosions of light and energy called supernovae - this galaxy is literally a gigantic multi-coloured light show, but definitely not on human timescales!"

"In order to sustain this rate of supernova activity, massive, quickly evolving stars must form or be born at an equally rapid rate in NGC 6946," said Gemini North Associate Director, Jean-René Roy. "Its stars are exploding like a string of firecrackers!"

It is speculated that if just a million years of this galaxy's history were compressed into a time-lapse movie lasting a few seconds, there would be nearly constant outbursts of light as new stars flare into view, while old ones expire in spectacular explosions. Over the past century, eight supernovae have exploded in the arms of this stellar metropolis, occurring in 1917, 1939, 1948, 1968, 1969, 1980, 2002, and 2004.

"In order to sustain this rate of supernova activity, massive, quickly evolving stars must form or be born at an equally rapid rate. Stars in this galaxy are exploding like popcorn!" added Dr Johnson. But it is this extreme stellar birth-rate, not the supernovae, which lends the galaxy its blazingly colourful appearance.

By comparison, the average rate for such catastrophic stellar outbursts in the Milky Way is about one per century, and only four have been recorded over the last thousand years. The last known supernova went off in our galaxy in the constellation Ophiuchus in 1604.

Yet, it is the ubiquitous occurrence of starbirth throughout NGC 6946 and not its supernovae that lend this galaxy its blazingly colourful appearance. For reasons not completely understood, this galaxy experiences a much higher rate of star formation than all the large galaxies in our local neighbourhood. The prodigious output of stellar nurseries in this galactic neighbour eventually lead to accelerated numbers of supernova explosions.

Starbirth regions exist in most galaxies, particularly in spirals, and are obvious as clouds of predominantly hydrogen gas call H II regions. These areas coalesce over millions of years to form stars. Young, hot, massive stars formed in these regions emit copious amounts of ultraviolet radiation, which strips the electrons from hydrogen atoms in which they are embedded. When these ionized hydrogen atoms re-associate with electrons they radiate in a deep red colour (at a wavelength of 656.3 nanometres) as the electrons transition back to lower energy levels.

This Gemini image of NGC 6946 utilizes a selective filter specifically designed to detect the radiation emanating from the starbirth regions. Additional filters help to distinguish other details in the galaxy, including clusters of massive blue stars, dust lanes, and a yellowish core where older more evolved stars dominate.

NGC 6946 lies between 10 and 20 million light-years away in the constellation Cepheus, and was discovered by Sir William Herschel (1738-1822) on September 9, 1798. It continues to fascinate astronomers, who estimate that it contains about half as many stars as the Milky Way. They often use it to study and characterize the evolution of massive stars and the properties of interstellar gas. As viewed in the new Gemini optical image, we see only the "tip of the iceberg" of this galaxy. Its optical angular diameter is about 13 arcminutes, but viewed at radio wavelength at the frequency of neutral hydrogen (1420 Mhz or 21-cm line), it extends considerably more than the angular diameter of the Moon.

Source: PPARC

Explore further: Neutron star smashup seen for first time, 'transforms' understanding of Universe

Related Stories

Seeing the light of neutron star collisions

October 16, 2017

When two neutron stars collided on Aug. 17, a widespread search for electromagnetic radiation from the event led to observations of light from the afterglow of the explosion, finally connecting a gravitational-wave-producing ...

Astronomers discover unusual spindle-like galaxies

October 12, 2017

Galaxies are majestic, rotating wheels of stars? Not in the case of the spindle-like galaxies studied by Athanasia Tsatsi (Max Planck Institute for Astronomy) and her colleagues. Using the CALIFA survey, the astronomers found ...

Recommended for you

A new way to harness wasted methane

October 17, 2017

Methane gas, a vast natural resource, is often disposed of through burning, but new research by scientists at MIT could make it easier to capture this gas for use as fuel or a chemical feedstock.

Sunlight stimulates microbial respiration of organic carbon

October 17, 2017

Sunlight and microbes interact to degrade dissolved organic carbon (DOC) in surface waters, but scientists cannot currently predict the rate and extent of this degradation in either dark or light conditions. A recent study ...

Plasma optic combines lasers into superbeam

October 17, 2017

Since its introduction in the 1977 film "Star Wars," the Death Star has remained one of science fiction's most iconic figures. The image of Alderaan's destruction at the hands of the Death Star's superlaser is burned into ...

Fish respond to predator attack by doubling growth rate

October 17, 2017

Scientists have known for years that when some fish sense predators eating members of their species, they try to depart the scene of the crime and swim toward safer waters. This sensible behavior is exactly what evolution ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.