February 8 – Shining Bright

Today’s factismal: Most stars aren’t visible because they are too small and too cool.

If you think about stars, you probably think of those pretty lights in the night sky. But if you are an astronomer and you think of stars, then you think of size and temperature. That’s because big stars, like VY Canis Majoris, have a lot of fuel but they burn through it fast becoming super-hot and glowing a bright blue that slowly changes to red as they lose mass and cool off slightly. (And I do mean “slightly”; at its start, a hypergiant like VY Canis Majoris burns about 500,000 times as brightly as the Sun but it gradually drops to a mere 200,000 times before exploding into a nova.) But small stars, like Epsilon Indi BB, are so small that they can just barely sustain fusion at all; as a result, they give off very little visible light and most of their “shining” is done in the infrared (“heat”) portion of the spectrum. These stars are so small and dim that they aren’t visible to the naked eye; they are the candle to the big star’s searchlight. But the thing is that there are a lot more candles than there are searchlights. For every star you see at night, there are at least 100 more that are too small to be seen.

A look at the Milky Way using ultraviolet and infrared light (Image courtesy NASA)

A look at the Milky Way using ultraviolet and infrared light
(Image courtesy NRAO)

Big big or small, astronomers study them all. And here’s an image of what those stars look like when we peek at them using ultraviolet and infrared light. “Ordinary” stars that we can see at night glow a greenish white, where newborn and small stars heat up the surrounding dust and make it glow a bright violet for infrared and a startling purple for radio waves. If you’d l;ike to see more pictures like this, head over to the National Radio Astronomy Observatory website:
https://public.nrao.edu/gallery

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