The hypergiant star AG Carinae picked to celebrate the 31st anniversary of Hubble being deployed into orbit

AG Carinae (Image NASA, ESA and STScI)
AG Carinae (Image NASA, ESA and STScI)

A new photo of AG Carinae, a hypergiant star that belongs to the Luminous Blue Variable (LBV) class, captured by the Hubble Space Telescope has been released to celebrate the 31st anniversary of Hubble being deployed into orbit. The star is surrounded by a nebula formed by materials ejected from the star itself in a period in which instability caused one or more extremely powerful outbursts. The shell that was created is about five light-years across.

A little more than 20,000 light-years from Earth, the star AG Carinae has a mass estimated to be around 70 times the Sun’s for a brightness estimated to be around one million times the Sun’s. Despite these characteristics, it’s not normally visible to the naked eye due to the distance and the dust that partially obscures it.

Luminous Blue Variable (LBV) stars are also called S Doradus stars. S Doradus is a hypergiant star and one of the brightest stars in the Large Magellanic Cloud, a satellite dwarf galaxy of the Milky Way. Due to its characteristics, it stimulated the interest of astronomers to become the prototype object of an entire class of very rare stars, as less than 50 of them are known in the galaxies of the so-called local group. Stars with a mass that is tens of times the Sun’s consume their hydrogen at very high speeds and end their life in a supernova after a few million years.

AG Carinae is already a few million years old, so it still has little left to live in astronomical terms. The LBV phase lasts for a very short time from this point of view, estimated at some tens of thousands of years. In this phase, it slowly changes its brightness but also has some periods marked by very powerful outbursts. A few thousand years ago, a period of that kind led to the ejection of an amount of materials that could have a mass even greater than 10 times the Sun’s.

Now we see AG Carinae in a quiet period, but its stellar wind is still emitted at a speed of around one million km/h, about 10 times faster than the materials of the nebula that surrounds it. This means that the stellar wind collides with the nebula materials, pushing them even further outwards. The various shapes visible in the nebula were “sculpted” by the action of the stellar wind over time.

This new photo captured by the Hubble Space Telescope was generated using various optical frequency filters along with an ultraviolet frequency filter. The result is a series of shades of colors that characterize various materials. Red indicates hydrogen gas together with nitrogen gas. The structures in blue are dust clumps illuminated by AG Carinae’s light.

On April 25, 1990, the Hubble Space Telescope was put into orbit after being launched the day before. The largest program in the history of this extraordinary instrument, ULLYSES (Ultraviolet Legacy Library of Young Stars as Essential Standards), studies the ultraviolet light of young stars and how they affect the surrounding area. AG Carinae is certainly an interesting object of study from this point of view and in this case, also offers one of the breathtaking images captured by Hubble.

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