To celebrate the 31st anniversary of the launch of the Hubble Space Telescope, astronomers targeted one of the brightest stars in the galaxy, with a glowing halo of gas and dust. The price for the monstrous star’s opulence is “living on the edge.” The star, called AG Carinae, it’s waging a tug of war between gravity and radiation to prevent self-destruction.
The expanding layer of gas and dust that surrounds the star is about five light years wide, which equates to the distance from here to the closest star beyond the Sun, Proxima Centauri.
The huge structure was created from one or more giant eruptions about 10,000 years ago. The outer layers of the star flew into space, like a boiling kettle peeling off its lid. The ejected material is roughly 10 times the mass of our Sun, NASA reports.
These bursts are the typical lifespan of a rare race of stars called the luminous blue variable, 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 roughly 10,000 million years of life of our Sun. AG Carinae is a few million years old and resides 20,000 light years away within our Milky Way galaxy.
The blinding glow of a million suns
The luminous blue variables exhibit a dual personality: They seem to spend years in idle bliss and then erupt in a smug outburst. These giants are stars in the extreme, very different from normal stars like our Sun. In fact, it is estimated that AG Carinae it is up to 70 times more massive than our Sun and shines with the blinding brilliance of a million suns.
“I like studying these types of stars because I am fascinated by their instability. They are doing something strange,” said Kerstin Weis, an expert in luminous blue variables at the Ruhr University in Bochum, Germany. Large bursts like the one that produced the nebula occur once or twice during the life of a luminous blue variable. A luminous blue variable star only spews material when it is in danger of self-destruction as a supernova. Due to their massive shapes and super hot temperatures, luminous blue variable stars like AG Carinae are in a constant battle to maintain stability.
“I like studying these types of stars because I am fascinated by their instability. They are doing something strange”, Kerstin Weis.
It is a fight of open arms between the pressure of radiation from inside the star pushing outward and gravity pushing inward. This cosmic coincidence results in the star expanding and contracting. The outside pressure occasionally wins the battle, and the star expands to such an immense size that it peels off its outer layers, like an erupting volcano. But this outburst only happens when the star is about to fall apart. After the star expels the material, it shrinks to its normal size, settles down again, and becomes dormant for a time.
Like many other luminous blue variables, AG Carinae remains unstable. It has experienced minor outbursts that have not been as powerful as the one that created the current nebula.
Although inactive, it continues to emit searing radiation
Although AG Carinae is dormant now, like a superhot star, it continues to emit fiery radiation and a powerful stellar wind (streams of charged particles). This outflow continues to shape the ancient nebula, sculpting intricate structures as the flowing gas hits the slower-moving outer nebula.
The wind travels at a speed of up to a million kilometers per hour, about 10 times faster than the expanding nebula. Over time, the hot wind reaches the cooler ejected material, hits it, and carries it further away from the star. This “snowplow” effect has cleared a cavity around the star. The red material is incandescent hydrogen gas mixed with nitrogen gas. The fuzzy red material in the upper left indicates where the wind has passed through a faint region of material and carried it into space.
The most prominent features, highlighted in blue, are tadpole-shaped filamentous structures and twisted bubbles. These structures are masses of dust illuminated by the reflected light from the star. The tadpole-shaped features, most prominent on the left and in the background, are denser accumulations of dust that have been sculpted by the stellar wind. Hubble’s keen vision reveals these delicate-looking structures in great detail.
Hubble is ideal for ultraviolet light observations because this wavelength range can only be seen from space.
The image was taken with visible and ultraviolet light. Ultraviolet light offers a slightly clearer view of the filamentous dust structures that extend up to the star. Hubble is ideal for ultraviolet light observations because this wavelength range can only be seen from space.
Massive stars, like AG Carinae, are important to astronomers because of their far-reaching effects on their surroundings. The largest program in Hubble’s history, the Young Stars Ultraviolet Legacy Library as Essential Standards, he’s studying the ultraviolet light from young stars and the way they shape their surroundings.
Luminous blue variable stars are rare: fewer than 50 are known among galaxies in our local group of neighboring galaxies. These stars spend tens of thousands of years in this phase, the blink of an eye in cosmic time. Many are expected to end their lives in titanic supernova explosions, which enrich the universe with elements heavier beyond iron.