Vibrations from ancient star reveal age of galactic collision

Vibrations from a bright star visible to the naked eye reveal the Milky Way had a colossal collision with a dwarf galaxy more than 11.5 BILLION years ago

  • Scientists studied oscillations from ‘ν Indi’ star collected by NASA and ESA 
  • These vibrations reveal secrets in the galaxy’s history such as their evolution 
  • When our galaxy hit the Gaia-Enceladus galaxy the star’s motion was altered 

A star that is visible from Earth with the naked eye has revealed that our Milky Way ingested a smaller galaxy at least 11.6 billion years ago.

Using data from NASA and ESA satellites, an international team were able to measure the oscillations of the star, called ν Indi, which is viewable from the Southern Hemisphere.

The team used these oscillation measurements – known as asteroseismology – to date the collision between the Milky Way and another dwarf galaxy.

The team found ν Indi was born early in the life of the Milky Way, but after the collision with the galaxy – known as Gaia-Enceladus – its motion was altered.

The astronomers believe the merger of Gaia-Enceladus and Milky Way began somewhere between 11.6 billion and 13.2 billion years ago, after ν Indi formed.

The precursor of the Milky Way merged with one of its then companions, Gaia-Enceladus

‘Since the motion of v Indi was affected by the Gaia-Enceladus collision, the collision must have happened once the star had formed,’ said Bill Chaplin, professor of astrophysics at the University of Birmingham and lead author on the study.

‘That is how we have been able to use the asteroseismically-determined age to place new limits on when the Gaia-Enceladus event occurred.’   

v Indi did not come from the other galaxy, but was born in our Milky Way.

But when the Milky Way collided with Gaia-Enceladus, the star’s motion was altered. 

V Indi bears the hallmarks of having been heated by the collision, which told the research team it must have already been in place before the merger.    

The Milky Way cannibalised a galaxy one quarter of its current mass about 11.6 to 13.2 billion years ago, according to new research

V Indi is just under 100 light years away in the constellation of Indus, which was first professionally surveyed by Europeans in the 16th Century. 

It’s a southern hemisphere constellation, so visible south of the equator, in countries such as Australia, Africa and South America. 

Scientists believe stars like v Indi are ‘fossilised records’ that carry information about the environments in which they are from, thanks to their long-lasting vibrations.

Astronomers believe that our own Milky Way galaxy is approximately 13.6 billion years old.

Over its lifetime, it has ingested many smaller galaxies but it has previously proved difficult to find the precise time at which any of these mergers occurred.

Researchers now conclude that the galactic merger of Gaia-Enceladus and the Milky Way most likely began as long ago as 13.2 billion years, which in relative terms makes the pre-merger Milky Way short-lived. 

‘Because we see so many stars from Gaia-Enceladus, we think it must have had a large impact on the evolution of our galaxy,’ said co-author Dr Ted Mackereth at the University of Birmingham.

‘Understanding that is now a very hot topic in astronomy, and this study is an important step in understanding when this collision occurred.’

Previous studies have revealed a population of stars that were engulfed through the collision of Gaia-Enceladus, which led to pollution of the chemical properties and formation of the Milky Way, including its inner stellar halo and thick disk.

‘This study demonstrates the potential of asteroseismology with TESS, and what is possible when one has a variety of cutting-edge data available on a single, bright star,’ said Professor Chaplin.

A previous study from last year estimated the collision as about 10 billion years ago, with the Gaia-Enceladus about 25 per cent the size of the current Milky Way before it was swallowed. 

This new study, led by the University of Birmingham, used data from NASA’s planet-hunting satellite called Transiting Exoplanet Survey Satellite (TESS), which was launched in 2018 specifically to survey stars outside our solar system.

This was then combined with information from the European Space Agency’s (ESA) Gaia mission, which was launched in 2013 to create a three-dimensional map of the Milky Way.  

WHAT IS THE EUROPEAN SPACE AGENCY’S GAIA PROBE AND WHAT IS DESIGNED TO DO?

Gaia is an ambitious mission to chart a three-dimensional map of our galaxy, the Milky Way, and in the process reveal its composition, formation and evolution.

Gaia has been circling the sun nearly a million miles beyond Earth’s orbit since its launch by the European Space Agency (ESA) in December 2013. 

On its journey, the probe has been discreetly snapping pictures of the Milky Way, identifying stars from smaller galaxies long ago swallowed up by our own.

Tens of thousands of previously undetected objects are expected to be discovered by Gaia, including asteroids that may one day threaten Earth, planets circling nearby stars, and exploding supernovas. 

Artist’s impression of Gaia mapping the stars of the Milky Way. Gaia maps the position of the Milky Way’s stars in a couple of ways. It pinpoints the location of the stars but the probe can also plot their movement, by scanning each star about 70 times

Astrophysicists also hope to learn more about the distribution of dark matter, the invisible substance thought to hold the observable universe together.

They also plan to test Albert Einstein’s general theory of relativity by watching how light is deflected by the sun and its planets.

The satellite’s billion-pixel camera, the largest ever in space, is so powerful it would be able to gauge the diameter of a human hair at a distance of 621 miles (1,000 km).

This means nearby stars have been located with unprecedented accuracy.

Gaia maps the position of the Milky Way’s stars in a couple of ways.

Gaia’s all-sky view of our Milky Way Galaxy and neighbouring galaxies, based on measurements of nearly 1.7 billion stars. The map shows the total brightness and colour of stars observed by the ESA satellite in each portion of the sky between July 2014 and May 2016. Brighter regions indicate denser concentrations of especially bright stars, while darker regions correspond to patches of the sky where fewer bright stars are observed. The colour representation is obtained by combining the total amount of light with the amount of blue and red light recorded by Gaia in each patch of the sky.

It pinpoints the location of the stars but the probe can also plot their movement, by scanning each star about 70 times.

This is what allows scientists to calculate the distance between Earth and each star, which is a crucial measure.

In September 2016, ESA released the first batch of data collected by Gaia, which included information on the brightness and position of over a billion stars.

In April 2018, this was expanded to high-precision measurements of almost 1.7 billion stars.

 

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