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Exploring Dwarf Galaxy Mysteries: DCT Science

On Saturday, July 21, the world-renowned Lowell Observatory will be holding a special star-studded event to celebrate "first light" of the brand new Discovery Channel Telescope (DCT).
/ Source: Discovery Channel

On Saturday, July 21, the world-renowned Lowell Observatory will be holding a special star-studded event to celebrate "first light" of the brand new Discovery Channel Telescope (DCT).

The DCT is a 4.3-meter telescope at an elevation of 7,760 feet (2,370 meters) atop a cinder cone in Happy Jack, 40 miles southeast of Flagstaff, Ariz. The telescope is a joint $53 million project between Lowell Observatory and Discovery Communications that took nine years to construct.

The huge telescope will be used to probe deep into the Kuiper Belt beyond the orbit of Neptune and explore intergalactic space, delving into the mysteries of dwarf galaxies.

PHOTOS: The Discovery Channel Telescope is Complete

To begin a special series of interviews based on the science that the DCT will focus on, Discovery News Space Producer Ian O'Neill spoke with Deidre Hunter, Lowell Observatory Astronomer and Deputy Director for Science, about the dwarf galaxy research she will undertake using the DCT to unravel these galaxies' most vexing secrets.

Ian O'Neill: What dwarf galaxy research are you currently working on?

Deidre Hunter: The main question that I'm currently trying to answer is: what drives star formation in dwarf galaxies? Galaxies like dwarf galaxies and spiral galaxies (i.e., the Milky Way) contain a lot of gas that occasionally accumulates to form clouds. Those clouds are then pulled together by gravity, making them denser and then fragment into stars. I'm interested in the process by which the clouds form in these dwarf galaxies. This is in order to understand how they are forming stars and how they are evolving with time.

IO: What are the biggest mysteries behind dwarf galaxies?

DH: The dwarf galaxies don't fit the models that tell us what's going on in spiral galaxies. There are several models that explain star formation in spiral galaxies, but they don't work for dwarf galaxies. They would predict that there should be no formation of stars in dwarf galaxies at all, and yet we see young stars in these galaxies; so we know they are forming stars but we don't understand what the primary processes are that form the clouds that, in turn, form the stars.

WATCH VIDEO: Making a massive mirror for the Discovery Channel Telescope.

HOWSTUFFWORKS: The Milky Way and Other Galaxies

IO: How will the Discovery Channel Telescope (DCT) be used to support your work?

DH: One of the things I want to use is a camera that we are currently building right now called LMI, which stands for Large Monolithic Imager, and only last week we received its CCD in the mail. So in the next month or so we hope to have a camera put on the backend of the DCT and one of the projects that has driven the design of this camera is the project that I want to do -- very deep imaging of a sample of dwarf galaxies and the idea is to look at the outer disk.

The dwarf galaxies are like disks, as spiral galaxies are disks, and as you go out from the center of the galaxy, the density of stars and the density of the gas drops. In the outer disk we see that there has been star formation and it has had star formation fairly recently. The centers of dwarf galaxies are hard to understand, but the outer disks are even harder to understand! So by looking in the outer disk of the dwarf galaxies, we can look at a very extreme environment for star formation and try to understand what's driving star formation out there.

So, the first step is to take images with the DCT camera and use different filters so we can look at the mix of stars that are in the outer disk and understand the history of star formation out there, find out how far out the stars go and characterize the outer disk of dwarf galaxies.

IO: What wavelengths will you be looking at?

DH: Ultraviolet, meaning around 3500 Angstroms (350 nm) and blue -- about 4000 Angstroms (400 nm) -- and green -- 5500 Angstroms (550 nm). So ultraviolet, blue and green.

IO: What would be your ideal science-run on the DCT look like? As in, what would you love to see in the data -- like an "ah-ha!" moment -- that would make you want to go out and have a party?

DH: Well, it's a lot of work to get to an "ah ha!" moment! So it doesn't just happen instantly. It would take a lot of processing of data. But I have already run a pilot project, so I've kind of already had the "ah-ha!" moment, which is that these disks (of the dwarf galaxies) go on for as long as we can detect them -- we don't see an "end" to the disk, it just peters-out as you go further out in radius. We also see that the stellar populations in the outer disks in a sample of a few galaxies look the same as it does in the inner part. So I think the really amazing thing would be to find that all dwarf galaxies have these same characteristics.

ANALYSIS: Dark Matter Mystery Unraveled by Dwarf Galaxies?

IO: A recent article based on Hubble observations of "ghost" dwarf galaxies mention that dwarf galaxies have a large amount of dark matter contained inside them. What makes these galaxies so dark matter "friendly"?

DH: The idea to come from models that simulate the beginning of the universe and consequent formation of the galaxies and so forth is that what actually comes out after the Big Bang are these dark matter "mini-halos." They have the mass of about that of a dwarf galaxy, so dwarf galaxies are basically all dark matter! And then, what happens over time in these simulations is that the baryonic matter -- the gas at the beginning of galaxy formation -- pools in nodes. At this point, the universe is just a filamentary structure of dark matter and the baryons travel along these filamentary structures and are pulled by gravity into these nodes -- this is where the galaxies themselves form. And so the dwarf galaxies -- from my naïve understanding of these complex simulations -- are these dark matter mini-halos with some baryonic matter has been attracted by gravity into the halo and then stars begin to form from the gas. They end up with a very large fraction of dark matter to luminous matter. The spiral galaxies, the giant galaxies, form as a result of taking lots of little galaxies and combining them together into bigger galaxies.