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Hubble spies rare giant star battling against self-destruction

May 3, 2021. Summarized by summa-bot.

Compression ratio: 29.5%. 1 min read.

In celebration of the 31st anniversary of the launching of NASA???s Hubble Space Telescope, astronomers aimed the renowned observatory at a brilliant ???celebrity star,??? one of the brightest stars seen in our galaxy, surrounded by a glowing halo of gas and dust. The price for its opulence is ???living on the edge.??? The giant star is waging a tug-of-war between gravity and radiation to avoid self-destruction. The star, called AG Carinae, is surrounded by an expanding shell of gas and dust. The nebula is about five light-years wide, which equals the distance from here to our nearest star, Alpha Centauri. The huge structure was created from one or more giant eruptions about 10,000 years ago, when our human ancestors were just beginning to farm. The star???s outer layers were blown into space???like a boiling teapot popping off its lid. The expelled material amounts to roughly 10 times our Sun???s mass. These outbursts are the typical life of a rare breed of star called a luminous blue variable (LBV), a brief convulsive phase in the short life of an ultra-bright, glamorous star that lives fast and dies young. These stars are among the most massive and brightest stars known. They live for only a few million years, compared to the roughly 10-billion-year lifetime of our Sun. AG Carinae is a few million years old and resides 20,000 light-years away inside our Milky Way galaxy. The star???s expected lifetime is between 5 million and 6 million years. Luminous blue variables exhibit a dual personality: They appear to spend years in quiescent bliss and then they erupt in a petulant outburst. These behemoths are stars in the extreme, far different from normal stars like our Sun. In fact, AG Carinae is estimated to be up to 70 times more massive than our Sun and shines with the blinding brilliance of 1 million suns. ???I like studying these kinds of stars because I am fascinated by their instability. They are doing something weird,??? said LBV expert Kerstin Weis of Ruhr University in Bochum, Germany. Major outbursts such as the one that produced the nebula occur once or twice during a luminous blue variable???s lifetime. An LBV star only casts off material when it is in danger of self-destruction as a supernova. Because of their massive forms and super-hot temperatures, luminous blue variable stars like AG Carinae are in a constant battle to maintain stability. It???s an arm wrestling contest between radiation pressure from within the star pushing outward and gravity pressing inward. This arm wrestling match results in the star expanding and contracting. The outward pressure occasionally wins the battle, and the star expands to such an immense size that it blows off its outer layers, like a volcano erupting. But this outburst only happens when the star is on the verge of coming apart. After the star ejects the material, it contracts to its normal size, settles back down, and becomes quiescent for a while. Like many other luminous blue variables, AG Carinae remains unstable. It has experienced lesser outbursts that have not been as powerful as the one that created the present nebula. Although AG Carinae is inactive now, its searing radiation and powerful stellar wind (streams of charged particles) have been shaping the ancient nebula, sculpting intricate structures as outflowing gas slams into the slower-moving outer nebula. The wind is travelling at up to 670,000 miles per hour (1 million km/hr), about 10 times faster than the expanding nebula. Over time, the hot wind catches up with the cooler expelled material, plows into it, and pushes it farther away from the star. This ???snowplow??? effect has cleared a cavity around the star. The red material is glowing hydrogen gas laced with nitrogen gas. The diffuse red material at upper left pinpoints where the wind has broken through a tenuous region of material and swept it into space. The most prominent features, highlighted in blue, are filamentary structures shaped like tadpoles and lopsided bubbles. These structures are dust clumps illuminated by the star???s reflected light. The tadpole-shaped features, most prominent at left and bottom, are denser dust that has been sculpted by the stellar wind. Hubble???s sharp vision reveals these delicate-looking structures in great detail. The image was taken in visible and ultraviolet light. Ultraviolet light offers a slightly clearer view of the filamentary dust structures that extend all the way down toward the star. Hubble is ideally suited for ultraviolet light observations because this wavelength range can only be viewed from space. Massive stars, like AG Carinae, are important to astronomers because of their far-reaching effects on their environment. The largest program in Hubble???s history???the Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES???will study the ultraviolet light of young stars and the way they shape their surroundings. Luminous blue variable stars are rare: less than 50 known among the galaxies in our local group of neighboring galaxies. These stars spend tens of thousands of years in this phase, a blink of an eye in cosmic time. Many are expected to end their lives in titanic supernova blasts, which enrich the universe with heavier elements beyond iron.

A rare blue giant star called AG Carinae, located 20,000 light-years from Earth in the Milky Way galaxy, has experienced explosive convulsions that created its distinctive halo. The Hubble Space Telescope imaged the star to celebrate 31 years since the observatory launched.

AG Carinae, a blue giant star located 20,000 light-years from Earth in the Milky Way galaxy, is one of those stars.

AG Carinae is one of the brightest stars in our galaxy -- radiating the light of 1 million suns -- and it's about 70 times more massive than our sun.

The star lashes out, expanding in size and releasing its outer layers into space.

This shell is five light-years wide, or the distance between Earth and its nearest star aside from the sun, known as Proxima Centauri.

These events occur once or twice for a star like AG Carinae.

Luminous blue stars like AG Carinae experience a relatively quiet period in the beginning, followed by a "convulsive" phase across their relatively short life span, astronomically speaking.

Hubble captured its latest image of AG Carinae in both visible and ultraviolet light, which reveals the intriguing structures around the star in great detail.

Scientists want to understand more about these rare stars, which usually end in giant supernova explosions that release heavy elements like iron into space.

by summa-bot

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