Scientists Have Discovered the Smallest Star Yet

Fagjun | Published 2017-07-13 06:30

A size comparison between Saturn and EBLM J0555-57Ab.
[Image by the University-of-Cambridge]

Astronomers have found the smallest star ever discovered. This is probably the smallest size that stars can be while still being stars.

We typically think of stars as large—larger than the largest planets. However, some stars can surprise us. The universe still holds a lot of secrets, and we're still discovering them one by one. What we know this time is that this special star, known as EBLM J0555-57Ab, is so small that it's smaller even that the already tiny TRAPPIST-1. TRAPPIST-1 is about the size of Jupiter, and thus significantly smaller than other stars. EBLM J0555-57Ab, meanwhile, is just a tad larger than Saturn. Even so, the star is 300 times more massive than the ringed planet. The gravity at its surface is also about 300 times the gravity that we feel on Earth.

However, the mass of EBLM J0555-57Ab counts for just about 8% of that of the sun. Thus, this small star just barely qualifies as a star.

Finding the Smallest Star in the Sky

Any less massive and EBLM J0555-57Ab would be a brown dwarf instead of a star.
[Image via nemesis maturity / YouTube]

If EBLM J0555-57Ab had less mass, astronomers would likely classify it as a brown dwarf. Brown dwarfs exist as something between a star and a gas giant. What, therefore, makes a star a star?

The presence of hydrogen fusion reaction at the core is the difference between a star and other bodies in space. A star has to have enough mass or more to sustain this fusion at its core. This is the reason why, if EBLM J0555-57Ab had even slightly less mass, it would no longer be a star.

EBLM J0555-57Ab is part of a binary system that lies about 600 light years away from Earth. Astronomers found out about the existence of EBLM J0555-57Ab when it passed in front of its larger companion star. The companion star dimmed at regular intervals, signifying that something else was orbiting around it. We have the planet-finding experiment called the Wide Angle Search for Planets (WASP) to thank for discovering the smallest star we know of so far.

Interestingly, the purpose of this program is to seek out exoplanets lurking around in the distance. It merely stumbled upon this momentous discovery. Then again, many other great discoveries were accidental or serendipitous.

The Knowledge a Single Star can Offer

EBLM J0555-57Ab and TRAPPIST-1
[Image by the University of Cambridge]

Astronomers can gain a wealth of knowledge from the discovery of the smallest star we know of at present. For one thing, we don't understand much about stars that are less than 20% the sun's mass. This is in spite of the fact that stars of this size are the most numerous among all kinds of stars. They aren't as bright as other stars, and are therefore difficult to detect. Of course, this makes the discovery of EBLM J0555-57Ab even more momentous.

If we understand more about stars like EBLM J0555-57Ab we can also understand more about the planets that orbit them. For example, we can gain more knowledge about star systems like that of TRAPPIST-1. Consequently, we can learn more about the planets in the system, which have captivated scientists since their discovery. This proves that even the smallest star has a lot of things to offer.

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