NASA's Hubble Space Telescope has captured a spectacular stellar fireworks display in a small, nearby galaxy, which resembles a skyrocket, with a brilliant blazing head and a long, star-studded tail.
A firestorm of star birth is lighting up one end of the diminutive galaxy Kiso 5639. The dwarf galaxy is shaped like a flattened pancake, but because it is tilted edge-on, it resembles a skyrocket.
Kiso 5639 is a rare, nearby example of elongated galaxies that occur in abundance at larger distances, where we observe the universe during earlier epochs.
Astronomers suggest that the frenzied star birth is sparked by intergalactic gas raining on one end of the galaxy as it drifts through space.
"I think Kiso 5639 is a beautiful, up-close example of what must have been common long ago," said Debra Elmegreen of Vassar College in the US.
"The current thinking is that galaxies in the early universe grow from accreting gas from the surrounding neighbourhood. It's a stage that galaxies, including our Milky Way, must go through as they are growing up," Elmegreen said.
Observations of the early universe, such as Hubble's Ultra-Deep Field, show that about 10 per cent of all galaxies have these elongated shapes, and are collectively called "tadpoles."
But studies of the nearby universe have turned up only a few of these unusual galaxies, including Kiso 5639.
The development of the nearby star-making tadpole galaxies, however, has lagged behind that of their peers, which have spent billions of years building themselves up into many of the spiral galaxies seen today.
Elmegreen used Hubble's Wide Field Camera 3 to conduct a detailed imaging study of Kiso 5639.
The images in different filters unveil information about an object by dissecting its light into its component colours. Hubble's crisp resolution helped researchers analyse the giant star-forming clumps in Kiso 5639 and determine the masses and ages of the star clusters.
The researchers selected Kiso 5639 from a spectroscopic survey of 10 nearby tadpole galaxies. The observations showed that in most of those galaxies, including Kiso 5639, the gas composition is not uniform.
The bright gas in the galaxy's head contains fewer heavier elements (collectively called "metals"), such as carbon and oxygen, than the rest of the galaxy.
Stars consist mainly of hydrogen and helium, but cook up other "heavier" elements. When the stars die, they release their heavy elements and enrich the surrounding gas.
"The metallicity suggests that there has to be rather pure gas, composed mostly of hydrogen, coming into the star-forming part of the galaxy, because intergalactic space contains more pristine hydrogen-rich gas," Elmegreen said.
"Otherwise, the starburst region should be as rich in heavy elements as the rest of the galaxy," she said.
