National Astronomical Observatory of Japan

Ultra Faint Dwarf Elliptical Galaxy Boötes I


Ultra Faint Dwarf Elliptical Galaxy Bootes I

This dwarf galaxy in the constellation Boötes is one of the class of Ultra Faint Dwarf Galaxies, which have only been discovered very recently. The total luminosity is only 100,000 times that of the Sun. Among globular clusters there are objects with 1,000,000 times the luminosity of the Sun; which means that Ultra Faint Dwarf Galaxies are dimmer than globular clusters. But they are still considered galaxies. Boötes I is located 60.4 kiloparsecs(*) from Earth, in the direction of the constellation Boötes. Even though it is a dwarf galaxy, it appears spread across a wide area of the celestial sphere because it is so close. So to capture all of it in an image, we needed the wide field of view of Suprime-Cam on the Subaru Telescope. This galaxy doesn’t look like a blur of light the way most galaxies do. Instead many individual stars are spread throughout this picture. So how can we say that we know this is a galaxy? By making a color luminosity diagram from this image, we know that out there is a group of stars with ages similar to those found in a globular cluster. It is thought that this Dwarf Galaxy in the constellation Boötes is a left over from the innumerable dwarf galaxies from which the Milky Way formed.

* 1 parsec = 3.26 light years.

Text by: Nobuo Arimoto (Subaru Telescope)
Translation by: Ramsey Lundock (NAOJ)

Image Data

ObjectBoötes I (in the constellation Bootes)
TelescopeThe Subaru Telescope
InstrumentSuprime-Cam (Subaru Prime Focus Camera)
WavelengthsV band, Ic band
ExposureV (600 s), Ic (3000 s)
DateApril 4, 2008 (UT)
ObserverSakurako Okamoto (University of Tokyo)
CopyrightNational Astronomical Observatory of Japan


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