Bellatrix

Nailing down the distance to a star isn’t easy. New observations can show that earlier ones had it all wrong.

That seems to be the case with Bellatrix, the third-brightest star of Orion. It’s to the upper left of Orion’s three-star belt during the evening.

For a long time, astronomers thought Bellatrix and the stars of the belt were members of the same family. Like the stars of the belt, Bellatrix is big, bright, and heavy. It’s eight or nine times the mass of the Sun, and thousands of times the Sun’s brightness.

But measurements made more than a decade ago by a space telescope contradict that idea. While the stars of the belt are all more than a thousand light-years from Earth, Bellatrix is only about 250 light-years away. So there’s no way it could belong to the same family as the stars of the belt.

The star’s fate depends in part on its distance.

Its mass is thought to be about eight-and-a-half times the mass of the Sun. That puts it right along a dividing line. A star at that mass or heavier may explode as a supernova; much below that line and it’ll have a less spectacular demise.

If Bellatrix were a little farther than 250 light-years, that would make it a little heavier, which would make it more likely to blow up. At less than 250 light-years, though, it would be less massive — and less likely to explode. So even a slight change in its distance could make a big difference in the fate of this impressive star.

Script by Damond Benningfield