Hubble Telescope discovers star 1500 times larger than the Sun called Westerlund 1-26

Scientists with NASA and the European Space Agency (ESA) have identified what could be the largest star ever discovered, the Westerlund 1-26, which has a radius over 1,500 times that of our Sun.

The star more formally called a red supergiant is part of the Westerlund 1 star cluster, inhabiting a region of the galaxy not too far (all things being relative) from our corner of the Milky Way at 15,000 light years away.

NASA and the ESA just released a remarkable new image of Westerlund 1 taken by the Hubble Space Telescope.

Named after Swedish astronomer Bengt Westerlund who first identified the star cluster in 1961, Westerlund 1 is an example of a super star cluster, a gravitationally interconnected group of stars (sometimes containing thousands of stars) which were formed at roughly the same time from one giant molecular cloud.

Estimated to be about three million years old, Westerlund 1 is quite young by comparison (the Sun is 4.6 billion years old, for example) but contains an unusually high number of very large stars, including six yellow hypergiants and three other red supergiants along with the “monster” Westerlund 1-26. “If Westerlund 1-26 were placed where our sun is in our solar system, it would extend out beyond the orbit of Jupiter,” says the ESA in a release.

There are other stars in contention for the title of largest in the (known) universe, including UY Scuti with a potential size of 1,708 solar radii and NML Cygni estimated to be between 1,642 and a whopping 2,775 times the Sun’s radius.

Determining the exact size of stars can be difficult due to surrounding gas and dust, but regardless, these massive stars (of which astronomers say there are many more to be discovered) challenge the imagination.

The Sun itself is large enough to contain a million planets the size of the Earth, and yet it stands as one of the smaller stars in the galaxy. Fraser Cain, astronomer and publisher of Universe Today, points to the red supergiant Betelgeuse as a good comparison star.

“Located in the shoulder of Orion, this familiar red supergiant has a radius of 950-1200 times the size of the Sun, and would engulf the orbit of Jupiter if placed in our Solar System,” says Cain. “In fact, whenever we want to put our Sun’s size into perspective, we often use Betelgeuse to do it.”

This past month marked the 20th anniversary of the Hubble’s Space Telescope Imaging Spectrograph (STIS), an instrument that combines a camera with a spectrograph which separates light into its component wavelengths.

Installed in February, 1997, on a service mission to the Hubble, the STIS has been crucial to a wide range of discoveries, from figuring out the masses of black holes at the centres of galaxies to determining the makeup of the galactic halo surrounding the Milky Way to finding evidence of water on Jupiter’s moons.

In 2001, astronomers used Hubble’s STIS to detect the presence of sodium around the planet HD 209468 b in the Pegasus constellation, marking the first chemical analysis of an atmosphere of a planet beyond our solar system.

The Hubble itself was launched on April 25, 1990, and is still going strong. Jointly operated by NASA and the ESA, Hubble remains the only space telescope to be serviced by astronauts, having had four service missions to date.

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Below: Betelgeuse’s Size