Sagittarius A*: Black Hole at the Centre of our Galaxy imaged
- Scientists from the Event Horizon Telescope (EHT) facility revealed the first image of the black hole at the centre of our galaxy i.e. the Milky Way.
- The Milky Way is a spiral galaxy that contains at least 100 billion stars. Viewed from above or below it resembles a spinning pinwheel, with our sun situated on one of the spiral arms and Sagittarius A* located at the centre.
What is Sagittarius A*?
- Pronounced Sagittarius ‘A’ star, it refers to the believed location of the supermassive black hole in the centre of our galaxy.
- About 50 years ago, astronomers identified an area within the constellation of Sagittarius that was the strongest region of radio emission – thus making it the likely centre of the Milky Way.
- It possesses 4 million times the mass of our sun and is located about 26,000 light-years—the distance light travels in a year, 5.9 trillion miles (9.5 trillion km)—from Earth.
What is an event horizon?
- Black holes are extraordinarily dense objects with gravity so strong that not even light can escape, making viewing them extremely challenging.
- A black hole’s event horizon is the point of no return beyond which anything—stars, planets, gas, dust and all forms of electromagnetic radiation—gets dragged into oblivion.
- The closer someone came to a black hole, the greater the speed they would need to escape that massive gravity.
- The event horizon is the threshold around the black hole where the escape velocity surpasses the speed of light.
What are the recent observations?
- The image of Sagittarius A* (SgrA*) gave support to the idea that the compact object at the centre of our galaxy is indeed a black hole, strengthening Einstein’s general theory of relativity.
- The image was obtained using the EHT’s global network of observatories working collectively to observe radio sources associated with black holes.
- It showed a ring of light —super-heated disrupted matter and radiation circling at tremendous speed at the edge of the event horizon—around a region of darkness representing the actual black hole.
- This is called the black hole’s shadow or silhouette.
How did Einstein’s theory found its proof here?
- According to Einstein’s theory, nothing can travel faster through space than the speed of light.
- This means a black hole’s event horizon is essentially the point from which nothing can return.
- The name refers to the impossibility of witnessing any event taking place inside that border, the horizon beyond which one cannot see.
About EHT Facility
- EHT project is a large telescope array consisting of a global network of radio telescopes.
- It combines data from several very-long-baseline interferometry (VLBI) stations around Earth, which form a combined array.
- It provides an angular resolution sufficient to observe objects the size of a supermassive black hole’s event horizon.
- In 2019, the eHT facility made history by releasing the first-ever image of a black hole, M87* — the black hole at the centre of a galaxy Messier 87, which is a supergiant elliptic galaxy.
Prelims Take Away
- Black Hole
- Sagittarius A*
- VLBI stations