They are the sharpest images of our neighbouring galaxies ever produced.
Made using NASA’s Hubble Space Telescope, an international team of astronomers today revealed the most comprehensive, high-resolution ultraviolet-light survey of nearby star-forming galaxies.
The team combined new Hubble observations with archival Hubble images for 50 star-forming spiral and dwarf galaxies in the local universe.
These six images represent the variety of star-forming regions in nearby galaxies. The galaxies are part of the Hubble Space Telescope’s Legacy ExtraGalactic UV Survey (LEGUS), the sharpest, most comprehensive ultraviolet-light survey of star-forming galaxies in the nearby universe. The six images consist of two dwarf galaxies (UGC 5340 and UGCA 281) and four large spiral galaxies (NGC 3368, NGC 3627, NGC 6744, and NGC 4258). The images are a blend of ultraviolet light and visible light from Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys.
The project, called the Legacy ExtraGalactic UV Survey (LEGUS), has amassed star catalogs for each of the LEGUS galaxies and cluster catalogs for 30 of the galaxies, as well as images of the galaxies themselves.
To see the full catalogue, click here.
‘There has never before been a star cluster and a stellar catalog that included observations in ultraviolet light,’ said survey leader Daniela Calzetti of the University of Massachusetts, Amherst.
‘Ultraviolet light is a major tracer of the youngest and hottest star populations, which astronomers need to derive the ages of stars and get a complete stellar history.
‘The synergy of the two catalogs combined offers an unprecedented potential for understanding star formation.’
How stars form is still a vexing question in astronomy, experts say.
‘Much of the light we get from the universe comes from stars, and yet we still don’t understand many aspects of how stars form,’ said team member Elena Sabbi of the Space Telescope Science Institute in Baltimore, Maryland.
‘This is even key to our existence — we know life wouldn’t be here if we didn’t have a star around.’
The star cluster catalogs contain about 8,000 young clusters whose ages range from 1 million to roughly 500 million years old.
These stellar groupings are as much as 10 times more massive than the largest clusters seen in our Milky Way galaxy.
The galaxy NGC 4258: These images are a composite of separate exposures acquired by the WFC3 and ACS instruments on the Hubble Space Telescope. Several filters were used to sample narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter.
The star cluster catalogs contain about 8,000 young clusters whose ages range from 1 million to roughly 500 million years old. Pictured, NGC 3627
The star catalogs comprise about 39 million stars that are at least five times more massive than our Sun.
Stars in the visible-light images are between 1 million and several billion years old; the youngest stars, those between 1 million and 100 million years old, shine prominently in ultraviolet light.
The Hubble data provide all of the information to analyze these galaxies, the researchers explained.
‘We also are offering computer models to help astronomers interpret the data in the star and cluster catalogs,’ Sabbi said.
‘Researchers, for example, can investigate how star formation occurred in one specific galaxy or a set of galaxies. They can correlate the properties of the galaxies with their star formation.
‘They can derive the star-formation history of the galaxies.
‘The ultraviolet-light images may also help astronomers identify the progenitor stars of supernovas found in the data.’
The star catalogs comprise about 39 million stars that are at least five times more massive than our Sun.
NGC 3368, a Spiral galaxy in the Constellation Leo 35 million light-years away
One of the key questions the survey may help astronomers answer is the connection between star formation and the major structures, such as spiral arms, that make up a galaxy.
‘When we look at a spiral galaxy, we usually don’t just see a random distribution of stars,’ Calzetti said.
‘It’s a very orderly structure, whether it’s spiral arms or rings, and that’s particularly true with the youngest stellar populations.
WHAT DOES THE HUBBLE SPACE TELESCOPE DO?
The Hubble Space Telescope (pictured) recently captured a stunning image of a galaxy 20 million light years away
The Hubble Space Telescope was launched jointly by NASA and the European Space Agency.
The Hubble is a space-based and long-term observatory.
The Hubble observes ultraviolet wavelengths, which the atmosphere filters out, and it collects visible light.
‘The Hubble Space Telescope has made some of the most dramatic discoveries in the history of astronomy,’ a statement on the Telescope says.
The machinery sits more than 370 miles above earth.
It can pick up on light via its ‘eyes’, which are five times more focused than ground-based telescopes.
The Hubble focuses on areas in deep outer space ‘where some of the most profound mysteries are still buried in the mists of time’.
‘On the other hand, there are multiple competing theories to connect the individual stars in individual star clusters to these ordered structures.
‘By seeing galaxies in very fine detail – the star clusters – while also showing the connection to the larger structures, we are trying to identify the physical parameters underlying this ordering of stellar populations within galaxies.
‘Getting the final link between gas and star formation is key for understanding galaxy evolution.’
Pictured, UGC 5340, a dwarf galaxy 40 million light years away in the constellation Leo: One of the key questions the survey may help astronomers answer is the connection between star formation and the major structures, such as spiral arms, that make up a galaxy.
UGCA 281, a dwarf galaxy 18 million light-years away from Earth. The star catalogs comprise about 39 million stars that are at least five times more massive than our Sun.
‘The data in the star and cluster catalogs of these nearby galaxies will help pave the way for what we see with NASA’s upcoming infrared observatory, the James Webb Space Telescope, developed in partnership with ESA and the Canadian Space Agency (CSA),’ Sabbi said.
Webb observations would be complementary to the LEGUS views.
The space observatory will penetrate dusty stellar cocoons to reveal the infrared glow of infant stars, which cannot be seen in visible- and ultraviolet-light images.
‘Webb will be able to see how star formation propagates over a galaxy,’ Sabbi continued.
‘If you have information on the gas properties, you can really connect the points and see where, when, and how star formation happens.’