As you sit in front of the computer reading this, you’re riding along on the largest telescope in the universe (that we know of). Oh, we’re not all sitting on a huge reflecting dish or anything like that. But, we do share surface of the planet with hundreds of observatories. The result is that there isn’t a moment of the day when all parts of the sky in every direction aren’t being studied by a telescope somewhere, somehow. That’s pretty amazing until you stop to think about how many telescopes there are in the world — including all the amateur gear! And, if you rise up a few hundred km into space, we have another whole collection of space-based “eyes on the sky.”
The Big Island of Hawai’i is home to a great collection of observatories, among them the Gemini installation, the Keck Observatory, the James Clerk Maxwell Telescope, the University of Hawaii 2.3-meter telescope, and many others. The National Observatory of Japan has an installation up there with the others on Mauna Kea: the Subaru telescope. I used a couple of their lovely images in my book. Here’s their latest.
It’s the Sextans A galaxy, a dwarf Irregular galaxy — a close neighbor to the Milky Way at only 5 million light years away. Here’s what the Subaru folks have to say about their image:
“Young blue stars and older yellow and red stars shine against a dark sky like jewels in a treasure chest in this image of Sextans A from Subaru Telescope?s prime focus camera Suprime-Cam. Sextans A is a dwarf irregular galaxy belonging to a group of galaxies called the Antlia-Sextans group 5 million light years from Earth. Even though five million light years is quite distant (50 billion billion kilometers or 30 billion billion miles), only about 40 galaxies are closer to our own Milky Way galaxy than Sextans A. The Antlia-Sextans group is the closest neighbor of the Local Group, which includes both our own Milky Way the Andromeda Galaxy.
Irregular galaxies do not have a regular symmetric shape like spiral or elliptical galaxies. Dwarf irregular galaxies containing only 100 million to a billion stars are the most common type of irregular galaxy. One main characteristic of dwarf irregular galaxies, other than their shape, is vigorous ongoing star formation. Sextans A has a mass comparable to only 100 million stars, one thousandth of the Milky Way, but contains a comparatively large amount of gas and dust, the raw ingredients for stars and planets. In the center of Sextans A is a high concentration of neutral hydrogen gas that serves as a reservoir for the formation of new stars. The Suprime-Cam image shows both young stars (blue) old stars (red) near the center of Sextans A where there is a large reservoir of neutral hydrogen gas and star formation is most vigorous. The green color highlights hydrogen gas ionized by radiation (HII regions) from the blue-hot young stars.
Many dwarf irregular galaxies are surrounded by neutral hydrogen gas that extends far beyond where the galaxy?s starlight fades away. Observations with radio telescopes have confirmed that Sextans A is no exception. The origin of this hydrogen gas and its effect on star formation are still unsolved puzzles. Yutaka Komiyama from Subaru Telescope, the observer of Sextans A, is now working on a solution using the Suprime-Cam data.”
