I recently read that "Betelgeuse" turns into a white dwarf star and it will disappear from night sky in next?

It is possible that Betelgeuse will become a supernova, which will be the brightest ever recorded, outshining the Moon in the night sky. Considering its size and age of 8.5 million years, old for its size class, it may explode within the next few thousand years. Since its rotational axis is not toward the Earth and also because of its 640 light year distance, Betelgeuse's supernova will not cause a gamma ray burst in the direction of Earth large enough to damage its ecosystem.

Nobel Laureate Charles Townes announced evidence that 15 consecutive years of stellar contraction has been observed by UC Berkeley's Infrared Spatial Interferometer (ISI) atop Mt. Wilson Observatory in Southern California. Reported on June 9, 2009, the star has shrunk 15% since 1993 with an increasing rate. The average speed at which the radius of the star is shrinking over the last 15 years is approximately 470-490 miles per hour.

According to the university, Betelgeuse's radius is about 5.5 A.U.s, and the star's radius has shrunk by a distance equal to half an astronomical unit, or about the orbit of Venus. Some theorists have speculated that this behavior is expected for a star at the beginning of the gravitational collapse at the end of its life. When it does end, it will first go Nova, outshining the moon possibly, before collapsing down to the dwarf star phase, but it would most likely become a neutron star.

Betelgeuse weights 20 times the mass of the sun, so it will with certainty become a black hole after collapse. For a white dwarf star, the star needs to weight less than 1.44 times the mass of the sun.

While Betelgeuse was lately found to be much more instable and pulsating than initially known, it is still not known for how long it will stay that instable. It could be still millions of years left. It currently shrinks at extreme high speed (for what we know of stars, it could also still be possible, that our expectation/model of stars is wrong) since 1993, having lost 0.5 AU since and is currently 5.5 AU large. The energy emission of Betelgeuse varied extremely in the past, so such a strong collapse could be just the beginning of a new pulsation.

Betelgueuse is around 650 lightyears away, I think. So what they are assuming is that Betelgeuse has already become a white dwarf 250 years ago and in another 400 years the light of that event will finally reach us. Only then will it appear to be a white dwarf, supernova, black hole, neutron star etc... to us. Does that make sense?

Do you have a reference for this? I know that Betelgeuse's days are numbered, but I don't think astrophysics is precise enough to predict this accurately.