Astrophotography is one of the most enjoyable parts of space exploration, and there’s nothing like Hubble. It recently celebrated the 31st anniversary of its launch with a spectacular image of one of the most impressive stars in the sky – the AG Carinae. In the not too distant future, Hubble or a successor may be able to capture an even more spectacular rendering of the star as it goes into supernova.
AG Carinae, appropriately located in the constellation Carina, is one of the brightest stars in the sky, although its apparent brightness on Earth is somewhat reduced due to its 20,000 light-year distance from Earth. The star is famous for a number of reasons, including being one of only 50 bright blue variable stars known.
Video shows AG Carinae in all its glory.
Photo credit: NASA / ESA / STScI, Leah Hustak (STScI), Alyssa Pagan (STScI), Joseph DePasquale (STScI), Greg T. Bacon (STScI)
The bright blue variables are extremely short-lived and violent, barely balancing between exploding into a supernova and collapsing under their own weight into a black hole. As part of their life cycle, they occasionally send out a spectacular eruption that creates a kind of glowing envelope around them, as shown in the Hubble image by AG Carinae.
Breakouts like the one in the picture only occur once or twice in the life of a bright blue variable. They occur when the radiation pressure from inside the star expands it to such a large size that it pushes material out of itself and then falls back into a more stable state for possibly millions of years.
An older picture by AG Carinae comes from Hubble’s legacy archives and was processed by Judy Schmidt.
Photo credit: Judy Schmidt / Hubble
In the case of AG Carinea, this eruption occurred about 10,000 years ago and emitted about ten times the mass of the Sun and is about 5 light years in diameter, slightly more than the distance from the Sun to the Alpha Centauri system. The material from the explosion is then exposed to the immense solar winds coming from the supermassive star, which itself is still roughly 70 times the mass of the sun.
At speeds of up to 670,000 miles per hour, this solar wind is about ten times faster than the ejection, creating a “snow plow” effect that removes part of the area directly around the star. At points around the star, the wind broke through the material shadow and dispersed it even more, as shown by the faint red glow in the upper left part of the Hubble image.
Eta Carinae is another bright blue variable in the same direction as AG Carinae and is surrounded by the spectacular Homunculus Nebula.
Photo credit: Jon Morse (University of Colorado) and NASA’s Hubble Space Telescope
Other prominent features of the Hubble image are “tadpoles” and “bubbles” which are highlighted in blue. These features are clumps of dust that are denser than the rest of the ejecta and are caused in part by interactions with the same stellar wind.
The image itself was captured in both visible and ultraviolet light, which allows for a clearer view of the filaments of the material that surrounds AG Carinae. However, Hubble doesn’t just take pictures to create a dramatic effect. It is in the middle of the largest program in its history known as the Ultraviolet Legacy Young Star Library as Essential Standards (ULLYSES), which focuses on young stars like the blue luminous variables. With luck, the program could catch one of these extremely rare stars at the expected end – a shocking supernova explosion. If there is an up-to-date observation platform capable of capturing an event like this in all its glory, it is its Hubble.
Lecture on bright blue variables by Nolan Walborn.
Photo credit: Nolan Walborn & Hubble Space Telescope’s YouTube channel
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Spectacular image of the bright blue variable star AG Carinae released by Hubble for its 31st launch anniversary.
Photo credit: NASA, ESA, STScI