Stars like the Sun live for a long time; well over ten billion years. Compared to that, they form pretty quickly, collapsing out of a cloud of gas and dust and switching on nuclear fusion in the cores in just a few dozen million years, sometimes less. That’s why we see zillions of already-formed stars in the sky but comparatively few baby ones (in part, the same reason you see lots of adult humans in a city but few babies).

The nearest star-forming regions to us are a few hundred light-years away, close enough to study, but they tend to be choked with dust — clouds of tiny grains of silicates and carbonaceous molecules. These clouds are opaque to visible light, making it hard to study what’s going on inside them with most telescopes. 

HP Tau is one such star, forming in the nearby Taurus cloud. It’s about 550 light-years away, and still accreting material from the nebula around it. We know this because we see hydrogen around it glowing, which means it’s hot as it falls onto the star; otherwise the gas would be cold and it wouldn’t glow. Also, as stars form the amount of material falling onto them can change, affecting the brightness — and in fact HP Tau is a variable, meaning its brightness does change over time. Technically speaking HP Tau isn’t even a star yet, since it hasn’t started fusing hydrogen into helium in its core, so it’s a protostar.

It’s also a trinary system, with two other stars nearby in orbit. Given they’re all embedded in the gas from which they’re forming, you’d think this would make for a dynamic and spectacular image.

You’d be right.

This image is from Hubble Space Telescope, and shows HP Tau and its sister stars. Surrounding them is a curlicue of dust and gas. Sometimes the forming star is quite luminous and powerful enough to excite the atoms in the gas, making it glow. In this case, though, HP Tau is not all that bright, so the gas is neutral. So, instead of glowing, it’s reflecting the light from the stars inside it, giving it a bluish tint — red light isn’t reflected well, but blue light is. We say the light is scattered by the material, but still we call this a reflection nebula. Jargon is confusing sometimes.

HP Tau is only a little bit more massive than the Sun, but much larger in size (about 1.8 times wider than the Sun), puffed up because it still hasn’t settled down yet to become a true star. It’ll likely be a few million more years before that happens.

It’s faint, about 15^th magnitude (the faintest star you can see with your eye is about 10,000 times brighter), despite being so close to us. That’s likely due to all that dust dimming our view of it; I noticed it’s much brighter in infrared, which can penetrate the dust, so that tracks. I’ll note that in wider shots that material around the stars extends for a long way, again supporting the idea that there’s a lot of stuff between us and those stars.

This image isn’t “natural” color (red, green, and blue) but instead uses two of Hubble’s filters, one that lets through red light (colored blue in the image) and one in the near-infrared (red in the image). That means any star that looks red here is very red. I like the red star to the left; if you look closely you can see that there are two sets of diffraction spikes almost on top of each other, indicating this is a very close double star, likely a binary system (the difference being the former is when two stars just happen to appear near each other but one may be much farther away from us, and the latter when they are physically associated). 

This image was taken to look for planet-forming disks around very young nearby still-forming stars. The astronomers targeted 16 such objects in hopes that we see some of these disks edge-on, which can tell us a lot about the planetary system forming there, too. No paper has been published about these data, though, so I guess we’ll have to wait and see what’s what here. In the meantime, soak in the utter beauty of star birth, and marvel that we can see it at all.

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