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Milky Way’s big black hole flings star to infinity and beyond

Mark Dunn, November 13, 2019 6:45PM Herald Sun

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An artist’s impression of the S5-HVS1 ejection by Sagittarius A*. Picture: James Josephides (Swinburne Astronomy Productions) media_cameraAn artist’s impression of the S5-HVS1 ejection by Sagittarius A*. Picture: James Josephides (Swinburne Astronomy Productions)

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Australian scientists have identified a star spat out and flung into infinity* by our galaxy’s supermassive black hole.

The star is travelling at six million kmh, 10 times the speed of most stars.

The star was ejected from the black hole five million years ago, around the time our ancestors were just learning to walk upright.

It is moving so fast it will exit the Milky Way in about 100 million years and never return, Australian National University Emeritus Professor Gary Da Costa said.

media_cameraThe Milky Way in the night sky. The star is moving so fast it will exit the Milky Way in about 100 million years.

“We traced this star’s journey back to the centre of our galaxy, which is pretty exciting,” Prof Da Costa said, confirming a 30-year prediction that stars could be expelled from galaxies by black holes.

Sagittarius A*, the giant black hole at the centre of the Milky Way, has a mass equivalent to more than four million Suns.
“In astronomical terms, the star will be leaving our galaxy fairly soon and it will likely travel through the emptiness of intergalactic* space for an eternity*.”

VIDEO: How the star came to be flung away by Sagittarius A*. Credit: Sergey Koposov

Milky Way’s black hole hurls star to infinity

ANU’s Dr Dougal Mackey said the team spotted the fast-moving star accidentally while searching for the shredded remains of small galaxies orbiting the Milky Way.

“The star is only 29,000 light years away, quite close by galactic* standards, which means the team could measure its trajectory* very precisely,” Dr Mackey said.

Dr Thomas Nordlander, also from ANU, said supermassive black holes can separate two stars orbiting each other — which scientists call a binary* stellar* system — if the system gets too close to a black hole.

“If such a binary system approaches a black hole too closely, the black hole can capture one of the stars into a close orbit and kick out the other at very high speed,” Dr Nordlander said.

The speeding star, S5-HVS1, was found while astronomers researched shredded remains of ancient galaxies.

An international team from ANU, Macquarie University, the University of Sydney and UNSW, as well as researchers from the US, UK and Chile made the discovery using the 3.9m Anglo-Australian Telescope at the ANU Siding Spring Observatory near Coonabarabran, New South Wales.

Siding Springs Observatory in Warrumbungle National Park, is Australia's premier facility for optical and infrared astrophysics research. Pic Tourism NSW. media_cameraSiding Springs Observatory in Warrumbungle National Park, near Coonabarabran, New South Wales. Picture: Tourism NSW

This telescope is the best in the world for studying the sparsely* distributed stars in the outskirts of the Milky Way, due to its ability to take measurements for up to 400 targets at a time.

media_cameraPrince Charles (right) on October 16, 1974 at the opening of the Anglo-Australian Telescope at Siding Springs.

Follow-up observations made with the ANU 2.3m telescope played an important role in confirming the star’s extreme speed.

The study is published in the journal Monthly Notices of the Royal Astronomical Society.

GLOSSARY

  • infinity: forever, with no end
  • Sagittarius A*: the name of the giant black hole at the centre of the Milky Way. Its name includes the * at the end
  • intergalactic: travel between galaxies
  • eternity: infinity;forever, with no end
  • galactic: relating to a galaxy
  • trajectory: path followed by a flying object
  • binary: involving two things
  • stellar: to do with stars
  • sparsely: thinly

EXTRA READING

World first photo of a black hole revealed

Collision creates supermassive black hole

True shape of Milky Way discovered

Black hole bends starlight

QUICK QUIZ

  1. How fast is this star travelling?
  2. What is the mass of Sagittarius A* comparable to?
  3. What were the scientists looking for when they made this discovery?
  4. What is the star that was spat out called? How far away is it?
  5. Why was the Siding Spring telescope the best in the world for this task?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Name the star
H5-SVH1 is not a very interesting name for such an amazing star, so give the star a new and better name. Your name can help people understand why this star is so important and amazing or describe what is special about the star. You could name the star after someone or something that you think is similar to it.

Use your new name in a poster that will help other kids understand why you chose your new name.

Time: allow 30 minutes to complete this activity
Curriculum Links: English, Science, Visual Communication Design

2. Extension
Why is this an important discovery?

Write as many reasons as you can think of using information in the story to help you.

Time: allow 15 minutes to complete this activity.
Curriculum Links: English, Science

VCOP ACTIVITY
Journey of a star
The star that was recently spat out from the black hole has just booked an interview with Kids News to share its journey.

Create 5 questions for Kids News journalists to ask the star about its journey through the black hole, and the galaxy it came from.

See if you can use at least 3 different questions stems (ways to start your questions), and don’t forget to end with a question mark.

HAVE YOUR SAY: What would you like to see happen in space?
No one-word answers. Use full sentences to explain your thinking. No comments will be published until approved by editors.

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