CANDELS And Hubble Team Up To Tackle Cosmic Dust
Hubble seeks out cosmic dust to fill in gaps in our knowledge of stellar formation
Got dust? Don’t we all. It hides under our beds, collects on shelves and sneaks its way into our ordinary lives.Even on the Moon they had dust problems.While we consider this type of dust an annoyance, dust itself is critical to building stars and planets. A question which astronomers have been seeking to explain is how cosmic dust forms over time. The answer could help us to further understand galactic evolution – and the stars and planets contained within them.
When it comes to cosmic dust, University of Texas at Austin assistant professor Steven Finkelstein and colleagues are hard at work collecting “dust bunnies” by utilizing one of the largest Hubble Space Telescope projects to date. They’ll be observing dust in thousands of galaxies over a huge span of cosmic time. They are taking on nearly 3,000 galaxies seen 500 million to 1,500 million years after the Big Bang. In terms of cosmic time, this is only a moment after the initial event, when compared to the 13.7-billion-year age of the Universe. The project is called CANDELS: the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey.
“We don’t yet understand how galaxies build up their dust reservoirs,” Finkelstein said. “We know that dust builds up through time, but exactly when the formation of dust begins is unknown.”
Where do all of these studies come from? Many of the galaxy images came from the team’s ongoing Hubble observations: more than 900 orbits studying distant galaxies with the Wide Field Camera 3 (WFC3). They also include data from several other large Hubble galaxy surveys (including Great Observatories Origins Deep Survey (GOODS) and the Hubble Ultra-Deep Field survey). According to Finkelstein, previous studies with smaller surveys, including a portion of his own, seem to show that ancient galaxies were dust free. However, CANDELS has found that even at a very early epoch, massive galaxies were regular dust factories and have evidence of granulated carbon and silicon.
“We found something we wouldn’t expect,” Finkelstein said. “Although dust can form quickly, I don’t think many people expected galaxies at only 800 million years after the Big Bang to have a lot of dust. These observations caused us to change our thinking.”
This composite image is made up of an optical image (shown in blue) by Hubble Space Telescope as part of the GOODS survey, combined with an infrared Hubble image (red and green) taken in dedicated CANDELS observations. Credit: S. Finkelstein/CANDELS Collaboration/STScI/NASA
Taking a look at these antique dust bunnies isn’t going to be an easy task – even for the Hubble Space Telescope. Only a very tiny amount of information is able to be seen, but its enough to pick out color – a clue to the amount of dust any particular galaxy contains. In this case, a red galaxy is dust rich, while a blue one is dust poor. According to Finkelstein, the early, massive galaxies were probably forming stars for quite some time. These “heavy metal” dust elements weren’t created during the Big Bang, but came from inside the stars – a product of fusion. When a massive star exhausts its nuclear fuel, it goes supernova and forces the heavy elements throughout the galaxy. These heavy elements are the basis for the dust which CANDELS observes.
“These results are very interesting because they tell us that dust does form at early times,” he said. “This is important because the same elements that compose the dust grains are necessary for the formation of planets. Also, we think that dust is a key component in allowing hydrogen gas to form molecules, which is necessary for star formation.” What’s more, the team found that in between 800 million and 1.5 billion years after the Big Bang, “all galaxies — not just massive ones — get dusty,” Finkelstein said.
These new results have Finkelstein excited about what future observations will reveal. “The presence of dust means that a previous generation of stars has lived and died. So, when we can peer back to even farther later this decade with JWST [the James Webb Space Telescope], there should be a lot for us to see!”
Original Story Source: McDonald Observatory News Release. Submitted by Tammy Plotner for “Dave Reneke’s World of Space and Astronomy News”.
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