1
00:00:00,000 --> 00:00:04,797
MISSING DARK MATTER HUBBLE MYSTERY

2
00:00:04,797 --> 00:00:15,399
Dark matter is the invisible glue 
that holds the universe together. 

3
00:00:15,399 --> 00:00:18,958
"Galaxy Motion Simulation. Observed with Dark Matter (On left) and Predicted without Dark Matter (On Right.)"

4
00:00:18,958 --> 00:00:29,399
Most galaxies are rotating so fast that gravity 
generated by stars and gas alone can’t keep them together.

5
00:00:29,399 --> 00:00:42,044
They should have flown apart long ago.
Something we can’t see must glue them together: dark matter.

6
00:00:42,044 --> 00:00:51,517
Unlike observable matter, dark matter does not emit, 
absorb, or reflect light, making it hard to detect.

7
00:00:51,517 --> 00:01:05,184
Instead, astronomers look for the 
gravity signature of dark matter by 
observing its effects on galaxies.

8
00:01:05,184 --> 00:01:17,668
In 2018, galaxy NGC 1052-DF2 made headlines 
because it seemed to be missing dark matter.

9
00:01:17,668 --> 00:01:26,496
The observed number of stars in NGC 1052-DF2
accounted for most of the gravity.

10
00:01:26,496 --> 00:01:35,544
This unique galaxy contains a tiny fraction
of the dark matter astronomers expected.

11
00:01:35,544 --> 00:01:47,490
A galaxy lacking dark matter is an extraordinary 
claim. It upsets theories of galaxy formation and evolution. 

12
00:01:47,490 --> 00:01:54,060
Because this result was so unusual, 
some astronomers questioned it.

13
00:01:54,060 --> 00:02:10,308
They looked for other explanations. 
Could the galaxy be closer, and have fewer stars 
than its brightness suggested?

14
00:02:10,308 --> 00:02:25,373
It would also imply the galaxy had more dark matter, 
to balance the insufficient gravity due to fewer stars.

15
00:02:25,373 --> 00:02:38,992
In theory, if two galaxies are the same distance away, 
their brightness would differ from each other.

16
00:02:38,992 --> 00:02:45,239
But if the galaxy with fewer stars is brought closer…

17
00:02:45,239 --> 00:02:56,277
...both galaxies would appear to be the same brightness.

18
00:02:56,297 --> 00:03:07,061
Hubble collected more data to 
better measure the galaxy’s distance.

19
00:03:07,061 --> 00:03:20,000
The team targeted aging red stars whose 
peak brightness is used to determine distance.

20
00:03:20,000 --> 00:03:30,392
But the new Hubble measurements still found 
it was a distant galaxy as originally suspected.

21
00:03:30,392 --> 00:03:43,144
The mystery of why NGC 1052-DF2 is 
missing most of its dark matter still persists.

22
00:03:43,144 --> 00:03:47,727
[SILENCE]