Perched atop the 13,460-foot summit of Mauna Kea is the Subaru telescope. It’s one of more than a dozen telescopes dotting one of the best astronomy observation points in the world.

The telescope is back in the news today after an international team of researchers spotted what could be the faintest satellite galaxy ever found. Called Virgo I, it lies towards the direction of the constellation Virgo. And is one of about 50 satellite galaxies of the Milky Way discovered so far.

Researchers used Subaru’s Hyper Suprime-Cam to spot the faint galaxy. Imagine a gigantic digital camera and you’re on the right track. Here’s the camera.

hyper suprime camera

And the Wide Field Corrector Lens.

wide field corrector lens

What’s the pixel count on this sucker? 870 megapixels. The sensor is made up of 116 CCDs.

Hyper Suprime camera sensor

Hyper Suprime-Cam can capture an area of the sky as large as nine full moons in a single exposure with very little distortion. All thanks to the Corrector Lens designed and manufactured by Canon. Yep, that same Canon.

Did You Know: Subaru’s prime focus sits 15 meters above the primary mirror. The distance between the mirror and the prime focus point is what gives the Subaru telescope its wide field of view.

Here’s a better image showing how high above the primary mirror the Hyper Suprime-Cam sits.

Subaru telescope prime focus point

Virgo I

Researchers say Virgo I could be the faintest satellite galaxy found yet. But how faint is it? Virgo I has an absolute magnitude of -0.8 in the optical waveband. The researchers tell us how that absolute magnitude stacks up with other galaxies:

M31 (Andromeda Galaxy) = -21.77
Large Magellanic Cloud = -18.35
Small Magellanic Cloud = -17.02

Virgo I’s discovery isn’t about records. It’s about what researchers haven’t found yet. Finding this faint galaxy suggests there are many more faint dwarf satellite galaxies lurking around the Milky Way.

“This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way,” says Masashi Chiba from Tohoku University. “How many satellites are indeed there and what properties they have, will give us an important clue of understanding how the Milky Way formed and how dark matter contributed to it.”

The researchers explain the current thinking of how this works.

Standard models of galaxy formation in the context of the so-called cold dark matter (CDM) theory predict the presence of hundreds of small dark halos orbiting in a Milky Way-sized dark halo and a comparable number of luminous satellite companions. However, only tens of satellites have ever been identified. This falls well short of a theoretical predicted number, which is part of the so-called “missing satellite problem.”

The Subaru Strategic Survey was launched to search for these satellites. An early look at the data led to the discovery of Virgo I, and researchers will continue searching the sky for more satellites like it. As we find more satellite galaxies around the Milky Way, our understanding of how our home galaxy formed will only grow.



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