Out of a hundred billion stars in the universe, most of them are plain and humdrum, but astronomers over the years have found plenty of peculiar stars. Sometimes the stars, in a universe bound by the laws of physics, transgresses the ordinary and becomes bizarre.

The stars situated out of our reach appear spectacular from a distance, but some of them are going through or have already gone through really strange and baffling experiences. Here are the four unusual and most interesting stars that will startle you.

PSR J1841-0500: The star that disappears once in a while

PSR J1841-0500 was at first thought to be a regular pulsar. The scientists were studying this star for over a year, and when they were about to conclude the observations, it disappeared. After multiple tests, scientists concluded that the pulsar was no longer there. PSR J1841-0500 had turned off. Nearly 100 out of 2,000 known pulsars stop pulsating or emitting the radio pulses for about a few minutes to hours. It is known as "nulling". Scientists continued their search for this mystery star for nearly a year and a half, hoping it would return, and it eventually did in August 2011 (after 580 days).

Tabby's Star: The one that people considered to be an alien

This star is 1,200 light-years away in the Cygnus constellation. This otherwise ordinary star intrigued astronomers as a transiting object caused its light to dip by as much as 20 per cent. As per calculations, that object had to be something a lot bigger than a planet. Some scientists anticipated it to be a swarm of comets, while others thought it to be an alien. However, subsequent observations have discarded anything artificial. Instead, it appears to be just a debris field of dust.

Swift J1644+57: The star consumed by a black hole

In the constellation of Draco, located nearly 3.9 billion light-years away, something happened. We are all aware of "black holes" and how it destroys anything that comes near it. Well, this time, it was a star named Swift J1644+57. The event occurred in another galaxy. Scientists first noticed it when they received an enormous amount of γ-rays and X-rays from a previously quiet part of the universe. Further observations revealed that the beam was being emitted from the centre of another galaxy. Later it was concluded that the beam was transmitted by a "jet" released after a black hole consumed the star.

HD 140283: Probably older than the Universe

Our universe is 13.8 billion years old, and by all appearances, HD 140283 is 14.4 billion years old. The age of the star, informally called "Methuselah's star," has been estimated based on its brightness, composition, and distance. And the minimum estimated age of the star is 13.2 billion years, while the maximum estimated age is 14.4 billion years.

So, which star do you think is the oldest among all?