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1st Image Of Our Galaxy's Black Hole Heart
Live Science
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6/16/2025
The Event Horizon Telescope captured the first image of the Milky Way galaxy's supermassive black hole Sagittarius A* — our galaxy's "black hole heart."
Credit: ESO
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Tech
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00:00
Imaging a black hole seems like an impossible dream.
00:12
After all, they are black and do not emit light.
00:16
So how can we see them?
00:19
Well, with a telescope big enough,
00:21
we could at least see the immediate surroundings of the largest black holes.
00:25
The supermassive ones that are millions or even billions of times heavier than our sun.
00:32
Then we would be able to unveil some of the mysterious secrets these monsters hide.
00:39
Except that when you do the maths,
00:41
you find that to observe even the closest supermassive black holes,
00:45
you'd need a telescope the size of the Earth.
00:48
Something beyond our wildest dreams.
00:51
Or maybe not.
00:55
A few years ago, 300 astronomers from nearly 80 institutes across the globe
01:00
joined forces and found a way to create a telescope as large as our planet.
01:05
And they did it without using new mirrors, screws or steel.
01:09
Their Event Horizon Telescope, or EHT, is not a real telescope, but a virtual one.
01:16
The stroke of genius of the EHT collaboration was in using powerful radio telescopes that already exist,
01:31
including ALMA and APEX, co-owned by ESO.
01:35
They combined their observations in a way no one had ever attempted before,
01:41
with a technique called Very Long Baseline Interferometry.
01:45
This may sound like sci-fi, but it actually works, as the EHT team showed back in 2019.
01:54
That's when they revealed the supermassive object at the center of the M87 galaxy to the world.
02:06
The very first image of a black hole.
02:14
To understand exactly how hard that was, let us drop in some facts.
02:18
First of all, you should know that the EHT telescopes could not see the black hole itself, as it is invisible.
02:27
Rather, they picked up the radio signals from the hot glowing gas around it and imaged the shadow the black hole casts on it.
02:39
To do this, the telescope antennas in the EHT array had to be pointed to exactly the same position in the sky at exactly the same time.
02:47
The EHT can tell if one of these antennas is off by just a millimeter,
02:51
and if the timing is shifted by a trillionth of a second, even though the telescopes are located thousands of kilometers apart.
03:01
Imaging the black hole in M87 then required combining the observations of all telescopes in the network using interferometry.
03:12
This technique works best if you have many telescopes, which wasn't the case.
03:16
The team had eight observatories, though now the network has grown to 11.
03:27
So the EHT researchers had to develop special algorithms to be able to fill in the gaps and reconstruct their image.
03:35
It was like staring at a puzzle with most pieces missing, trying to figure out what the whole image would look like.
03:41
To determine if the result was scientifically bulletproof, they used a variety of methods.
03:48
Computer simulations to identify errors introduced by their telescope network,
03:53
different teams working in isolation on reconstructing the image in different ways,
03:58
new techniques and software.
04:00
It took years of work, until they were sure they had done it right.
04:03
Only then did they show their image to the world.
04:06
The result was like peering at the black hole in M87 with a telescope almost the size of the Earth,
04:24
an instrument so powerful that it could see details as small as a doughnut on the Moon.
04:36
So what's next for the EHT?
04:40
The team have already pointed their telescopes to a new target.
04:43
Sagittarius A star, the supermassive black hole at the heart of the Milky Way.
04:51
Our black hole.
04:56
Sagittarius A star is much closer to Earth than the supermassive black hole in M87.
05:02
So you may think that imaging it is a piece of cake by comparison.
05:06
Sorry to disappoint you.
05:08
It's even more difficult.
05:09
First, the centre of the Milky Way is obscured to us by clouds of dust and hot gas
05:17
that scatter the radio signals coming from around the black hole.
05:22
Furthermore, because Sagittarius A star is about 1500 times less massive than its cousin in M87,
05:29
its radio signals change far more rapidly in time.
05:33
Blobs of plasma orbited in just a few minutes,
05:35
whereas those in M87 orbit the black hole every few days.
05:42
This forces astronomers to adapt their algorithms and to develop new techniques to get stable images.
05:48
A bit like trying to read the brand on a basketball while spinning it on your finger.
05:53
In the end, the EHT team did manage to overcome all these obstacles.
06:01
So here it is.
06:03
The first image of Sagittarius A star, the black hole at the centre of the Milky Way.
06:08
the Milky Way.
06:10
The Milky Way
06:15
The Milky Way
06:18
The Milky Way
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4:05
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