Science

Hubble celebrates 31st birthday with a stunning photo of a giant star

To mark the 31st anniversary of the Hubble Space Telescope astronauts pointed it in the direction of a giant star that is ‘on the edge of destruction’. 

The giant star, named AG Carinae, featured in this latest image is waging a tug-of-war between gravity and radiation to avoid self-destruction. 

It is surrounded by an expanding shell of gas and dust, also known as a nebula, that has been shaped by the powerful winds of the giant star.

This nebula surrounding the star is about five light-years wide – roughly about the same distance between the sun and our nearest star Alpha Centauri.  

Hubble, a joint NASA and European Space Agency (ESA) project, launched for low Earth orbit in 1990 and has taken a ‘birthday image’ of a distant object every year. 

The giant star, named AG Carinae, featured in this latest image is waging a tug-of-war between gravity and radiation to avoid self-destruction

AG CARINAE: A LUMINOUS BLUE VARIABLE STAR 

AG Carinae is a luminous blue variable star about 19,570 light years away.

It’s one of the most luminous stars in the Milky Way at about a million times brighter than our own sun.

It is surrounded by a nebula of ejected gas and dust spreading out about five light years from the star.

  • Constellation: Carina
  • Mass: 55 times  the sun mass
  • Radius: 50-500 times the sun radius 
  • Temperature: 8,000 to 26,000 Kelvin

It is in a transitional stage between a blue supergiant and a Wolf-Rayet star.

Wolf-Rayet stars are among the hottest types of stars, reaching up to 210,000 K with intense winds. 

The huge structure surrounding AG Carinae was created from one or more giant eruptions several thousand years ago. 

The star’s outer layers were blown into space, the expelled material amounting to roughly 10 times the mass of our Sun. 

These outbursts are typical in the life of a rare breed of star called a Luminous Blue Variable (LBV), a brief unstable 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, living for just a few million years – compared to the 10 billion year lifespan of our own star.  

AG Carinae is a few million years old and resides 20,000 light-years away inside our Milky Way galaxy and will live for up to six million years.  

LBVs have a dual personality, appearing to spend years in semi-bliss and then erupting in a petulant outburst when their luminosity increases.  

The star is thought to be about 70 times more massive than the sun and shining up to a million times brighter than our own star.

Major outbursts such as the one that produced the nebula featured in the new Hubble image occur a few times during a LBV’s lifetime, cast off when it is in danger of self-destruction.

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 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 stable again.

LBV stars are rare with fewer than 50 known among the galaxies in our local group of neighbouring galaxies. 

These stars spend tens of thousands of years in this phase, a blink of an eye in cosmic time. Some are expected to end their lives in titanic supernova blasts, which enrich the Universe with the heavier elements beyond iron.

Pictured here is the region of the sky around the star AG Carinae, which is positioned in the centre of the image

Pictured here is the region of the sky around the star AG Carinae, which is positioned in the centre of the image

LUMINOUS BLUE VARIABLE STARS 

A luminous blue variable (LBV) star shows unpredictable and sometimes dramatic variations in brightness.

They are a form of massive evolved star also known as S Doradus variables.

LBVs are massive unstable supergiant and hypergiant stars with periodic outbursts and large eruptions. 

During a normal outburst temperature of the star drops by about 30%.

They can reach a maximum brightness a million times that of the sun, with sizes up to 100 times the mass of the sun. 

Like many other LBVs, 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 semi-quiescient now, its searing radiation and powerful stellar wind 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 1 million kilometres per hour, about 10 times faster than the expanding nebula. Over time, the hot wind catches up with the cooler expelled material, ploughs into it, and pushes it farther away from the star.  

The red material seen in the image, at the outer edge of the nebula, is glowing hydrogen gas laced with nitrogen gas.  

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 light. The tadpole-shaped features, most prominent at left and bottom, are denser dust clumps that have been sculpted by the stellar wind. 

Hubble’s sharp vision reveals these delicate-looking structures in great detail. 

For its 30th anniversary Hubble captured an imaged dubbed the ‘cosmic reef’ due to the resemblance it had to an underwater world. 

It showed the giant red nebula NGC 2014 and its smaller blue neighbour NGC 2020 belonging to the Large Magellanic Cloud, a satellite galaxy of the Milky Way.

NASAs Hubble Space Telescope is still working and has made more than 1.3 million observations since its mission began in 1990

The Hubble telescope was launched on April 24, 1990, via the space shuttle Discovery from Kennedy Space Centre in Florida.

It is named after famed astronomer Edwin Hubble who was born in Missouri in 1889.

He is arguably most famous for discovering that the universe is expanding and the rate at which is does so – now coined the Hubble constant. 

The Hubble telescope is named after famed astronomer Edwin Hubble who was born in Missouri in 1889 (pictured)

The Hubble telescope is named after famed astronomer Edwin Hubble who was born in Missouri in 1889 (pictured)

Hubble has made more than 1.3 million observations since its mission began in 1990 and helped publish more than 15,000 scientific papers.

It orbits Earth at a speed of about 17,000mph (27,300kph) in low Earth orbit at about 340 miles in altitude.

Hubble has the pointing accuracy of .007 arc seconds, which is like being able to shine a laser beam focused on Franklin D. Roosevelt’s head on a dime roughly 200 miles (320km) away.

The Hubble telescope is named after Edwin Hubble who was responsible for coming up with the Hubble constant and is one of the greatest astronomers of all-time

The Hubble telescope is named after Edwin Hubble who was responsible for coming up with the Hubble constant and is one of the greatest astronomers of all-time

Hubble’s primary mirror is 2.4 meters (7 feet, 10.5 inches) across and in total is 13.3 meters (43.5 feet) long – the length of a large school bus.

Hubble’s launch and deployment in April 1990 marked the most significant advance in astronomy since Galileo’s telescope. 

Thanks to five servicing missions and more than 25 years of operation, our view of the universe and our place within it has never been the same. 


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