VV Cephei

VV Cephei is an eclipsing binary star system. A binary star system is pair of stars orbiting about their common center of mass. Some of these systems are described as eclipsing due to their nature of occasionally obstructing their partner from an observer on Earth. This can happen when these systems’ orbital plane lies near the observer’s line of sight.

Found in the constellation Cepheus, some 2,400 light years away from Earth, VV Cephei is made up of the hypergiant VV Cephei A and VV Cephei B, the blue main sequence star. The distance between the two stars is, on the average, 25 AU (astronomical units). Because of its high eccentricity, this distance can change between 17 and 34 AU.

Eccentricity is a measure of an orbit’s deviation from a perfect circle, where a high eccentricity means a large deviation and a low eccentricity means a small deviation.

Among all recorded stars, VV Cephei A is known to be the second largest in the Milky Way and the 3rd overall. Its diameter is at least 1,600 times wider than the Sun’s, while its luminosity is at least 280,000 times greater. To give you an idea how large that is, imagine a star so huge, that if we replaced our own sun with it, it would occupy a space that would extend way past Jupiter’s orbit.

It’s smaller partner, VV Cephei B, on the other hand, is only about 10 times larger than the Sun and about 100,000 times as luminous.

One complete orbit of this system lasts for about 7,430 days or 20.3 years, with the eclipse lasting about 1,300 days. A total eclipse of this system takes about 40% of that time.

Much of the information known about VV Cephei, including those written above are very rough estimates. For example, its distance is too far away from us to use parallax, the triangulation method used to measure large distances in astronomy. The estimated distance of 2,400 light years is based upon the speculation that this binary star system belongs to the Cepheus OB2 association of hot blue stars, whose distance from us is somewhere around that value.

Some observers believe that VV Cephei A is nearing its end, and will soon depart by way of a supernova. Presumably, this will eventually leave VV Cephei B by its lonesome.

We have some related articles here that may interest you:

• Cepheus
• What is a Binary Star?

There’s more about it at NASA. Here are a couple of sources there:

• What is a Binary Star System?
• Why are binary stars interesting?

Here are two episodes at Astronomy Cast that you might want to check out as well:

• Where Do Baby Stars Come From
• Where Do Stars Go When they Die?

Reference:
Wikipedia

Tagged as: binary star, Cepheus, VV Cephei