24 October 2016 | Sirius B

Sirius B

Credit: Tommaso Nicolò | Click image to enlarge


This image of Sirius and Sirius B was made by 22-year-old Tommaso Nicolò from Italy who started developing interest in the universe from the young age of 5. He used a DSLR connected to a telescope to film this binary system and stacked the individual frames to create this image.

Sirius B is the name of the fainter, smaller, less massive star in the Sirius binary system (the brighter, larger, more massive one is Sirius A, or just Sirius). It was hypothesized to exist almost eighteen years before it was actually observed!

Friedrich Bessel, a German astronomer, analyzed data on the position of Sirius (Bessel was the one who first observed stellar parallax and is known for the Bessel functions), in particular its proper motion, and concluded – in 1844 – that there was an unseen companion star (the same principle used to infer the existence of Neptune, around the same time). In 1862 Alvan Clark saw this companion, using the 18.5″ refracting telescope he’d just built (quite a feat; Sirius B is ~10 magnitudes fainter than Sirius A, and separated by only a few arcseconds).

Sirius B is a white dwarf, one of the three “classics”, discovered to be white dwarf stars in the early years of the 20th century (Sirius B was the second to be discovered – 40 Eridani B had been found much earlier, and Procyon B was also hypothesized by Bessel (in 1844) though not observed until much later (in 1896)). It is one of the most massive white dwarfs so far discovered; its mass is the same as that of the Sun (approximately). Like all white dwarfs, it is small (it has a radius of only 0.008, compared with the Sun’s, which makes it smaller than the Earth!); like most seen so far, it is hot (approx 25,000 K).

Source: Universe Today

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