Browse content similar to Guide to the Galaxy. Check below for episodes and series from the same categories and more!
Line | From | To | |
---|---|---|---|
This is the first map of the Milky Way | 0:00:06 | 0:00:08 | |
made by William Herschel back in 1785 | 0:00:08 | 0:00:11 | |
in a paper he called On The Construction Of The Heavens. | 0:00:11 | 0:00:15 | |
And it's a wonderful thing, but it's not that accurate. | 0:00:15 | 0:00:18 | |
It shows the sun at the centre, which is wrong. | 0:00:18 | 0:00:20 | |
There are no spiral arms. | 0:00:20 | 0:00:21 | |
But he did get one important thing right. | 0:00:21 | 0:00:23 | |
He shows the Milky Way as a disc seen almost side on. | 0:00:23 | 0:00:27 | |
Since then, our knowledge of the Milky Way has greatly improved, | 0:00:27 | 0:00:31 | |
but these images are actually artists' impressions. | 0:00:31 | 0:00:34 | |
We think that the Milky Way looks like this, | 0:00:34 | 0:00:36 | |
but we don't know for certain. | 0:00:36 | 0:00:37 | |
In fact, we know surprisingly little about our home galaxy. | 0:00:37 | 0:00:41 | |
But a revolution in our understanding | 0:00:41 | 0:00:43 | |
of the Milky Way is underway, | 0:00:43 | 0:00:45 | |
and the more we learn about our galaxy, | 0:00:45 | 0:00:47 | |
the more surprising and interesting it becomes. | 0:00:47 | 0:00:50 | |
So tonight, we bring you the bang up-to-date Guide To Our Galaxy | 0:00:50 | 0:00:54 | |
with the most exciting and unusual discoveries. | 0:00:54 | 0:00:56 | |
Welcome to The Sky At Night. | 0:00:56 | 0:00:58 | |
Like all good guides, ours will include | 0:01:24 | 0:01:27 | |
the best maps available, | 0:01:27 | 0:01:28 | |
the most interesting destinations | 0:01:28 | 0:01:30 | |
and, of course, a bit of history. | 0:01:30 | 0:01:32 | |
We'll be joined by guest presenter | 0:01:32 | 0:01:35 | |
Neil deGrasse Tyson for a tour | 0:01:35 | 0:01:38 | |
of his top five strange and spectacular stars. | 0:01:38 | 0:01:42 | |
This white dwarf is effectively flaying | 0:01:42 | 0:01:45 | |
the outer layers of this giant, | 0:01:45 | 0:01:47 | |
consuming it, body and soul. | 0:01:47 | 0:01:50 | |
Pete will show us how to find some of the highlights of our galaxy | 0:01:51 | 0:01:54 | |
in the night sky. | 0:01:54 | 0:01:56 | |
But first, we're going to start | 0:01:57 | 0:01:59 | |
with the most essential part of any guide, the map. | 0:01:59 | 0:02:03 | |
We're here at the Institute of Astronomy in Cambridge, | 0:02:03 | 0:02:05 | |
where the researchers have been making the most detailed | 0:02:05 | 0:02:08 | |
and the most accurate map of the Milky Way ever. | 0:02:08 | 0:02:11 | |
To do that, they're using one of the most impressive space telescopes | 0:02:11 | 0:02:14 | |
ever constructed. If it were here on Earth, | 0:02:14 | 0:02:17 | |
it would be capable of measuring the thickness of a coin on the moon. | 0:02:17 | 0:02:20 | |
In December 2013, | 0:02:23 | 0:02:25 | |
the European Space Agency launched the Gaia space telescope. | 0:02:25 | 0:02:29 | |
Its mission - to map the stars of the Milky Way | 0:02:31 | 0:02:33 | |
in unprecedented detail. | 0:02:33 | 0:02:35 | |
Gaia is actually two telescopes, | 0:02:39 | 0:02:41 | |
each observing 100,000 stars per hour | 0:02:41 | 0:02:45 | |
and capturing the data with a one billion pixel camera, | 0:02:45 | 0:02:49 | |
giving Gaia resolution that is ten times greater | 0:02:49 | 0:02:52 | |
than most ground-based telescopes. | 0:02:52 | 0:02:54 | |
Over its five-year mission, | 0:02:56 | 0:02:58 | |
Gaia will observe each part of the sky 70 times | 0:02:58 | 0:03:02 | |
in order to measure the exact positions of the stars, | 0:03:02 | 0:03:05 | |
their distances and their motions. | 0:03:05 | 0:03:07 | |
This room is where data from Gaia comes pouring in and gets processed. | 0:03:09 | 0:03:13 | |
It's effectively the nerve centre for understanding our galaxy. | 0:03:13 | 0:03:17 | |
You get some idea | 0:03:20 | 0:03:21 | |
of the scale of the data-processing operation in here. | 0:03:21 | 0:03:25 | |
This supercomputer is made up of 1,296 processing cores... | 0:03:25 | 0:03:30 | |
..but this is just the tip of the iceberg. | 0:03:32 | 0:03:34 | |
There are five more centres like this dotted around Europe, | 0:03:35 | 0:03:38 | |
all handling Gaia's data. | 0:03:38 | 0:03:40 | |
To convert raw satellite data from Gaia | 0:03:43 | 0:03:46 | |
into an actual map of the Milky Way | 0:03:46 | 0:03:48 | |
with precise positions, distances and brightnesses is no mean feat. | 0:03:48 | 0:03:53 | |
In fact, for the first batch alone, | 0:03:53 | 0:03:54 | |
they've had to analyse around 120 billion images. | 0:03:54 | 0:03:58 | |
And to achieve the incredible precision | 0:04:00 | 0:04:02 | |
required by the Gaia mission, | 0:04:02 | 0:04:04 | |
the data-processing teams have to try to correct | 0:04:04 | 0:04:07 | |
for every possible source of error. | 0:04:07 | 0:04:09 | |
They even have to account for the gravitational influence | 0:04:09 | 0:04:12 | |
of the other planets in the solar system on the light from the stars. | 0:04:12 | 0:04:17 | |
It's a tremendous task, | 0:04:17 | 0:04:19 | |
so much so that it took a year to process | 0:04:19 | 0:04:21 | |
the first 14 months' worth of data. | 0:04:21 | 0:04:23 | |
But it's been worth all the effort, | 0:04:25 | 0:04:27 | |
because the result is nothing less | 0:04:27 | 0:04:29 | |
than the first truly accurate map of our home galaxy. | 0:04:29 | 0:04:33 | |
And Chris went to meet lead scientist Gerry Gilmore | 0:04:33 | 0:04:36 | |
to see the map for himself. | 0:04:36 | 0:04:39 | |
So, Chris, welcome to our new map of our Milky Way. | 0:04:39 | 0:04:43 | |
It's beautiful. | 0:04:43 | 0:04:44 | |
You can see immediately the sort of big picture structure. | 0:04:44 | 0:04:48 | |
First thing to notice is that this | 0:04:48 | 0:04:50 | |
is a map of the entire sky. | 0:04:50 | 0:04:51 | |
But this stripe across the middle, | 0:04:51 | 0:04:53 | |
this bright stripe, that's the galaxy. | 0:04:53 | 0:04:55 | |
That's the Milky Way galaxy, that's right, yes. | 0:04:55 | 0:04:58 | |
But there is more to the Milky Way than just the main disc. | 0:04:58 | 0:05:01 | |
There are also millions of stars, both above and below the disc. | 0:05:01 | 0:05:06 | |
Everything white that you can see in this image is starlight. | 0:05:06 | 0:05:09 | |
What we need to do is zoom in. | 0:05:10 | 0:05:12 | |
This is the top-layer map, and now we are zooming in. | 0:05:12 | 0:05:16 | |
So this is the inner parts of the Milky Way here, | 0:05:16 | 0:05:18 | |
these big dust clouds and dust lanes, | 0:05:18 | 0:05:20 | |
the dust lane, these are dust lanes, | 0:05:20 | 0:05:22 | |
and you start to see that all the white light | 0:05:22 | 0:05:25 | |
is now breaking up into stars, | 0:05:25 | 0:05:27 | |
into individual stars. | 0:05:27 | 0:05:29 | |
So, as you get further in, as we zoom in, | 0:05:29 | 0:05:31 | |
we see more and more stars individually. | 0:05:31 | 0:05:34 | |
Look at how they suddenly appear | 0:05:34 | 0:05:36 | |
as you go that little bit deeper into space and, ping! | 0:05:36 | 0:05:38 | |
What you thought was just white light is actually starlight. | 0:05:38 | 0:05:42 | |
And how many stars are there in the galaxy? | 0:05:42 | 0:05:44 | |
There's maybe 100 billion, 200 billion, 300 billion. | 0:05:44 | 0:05:48 | |
The number's probably near the high end of that range. | 0:05:48 | 0:05:50 | |
What we know is that there's maybe twice as many | 0:05:50 | 0:05:52 | |
as we previously thought. | 0:05:52 | 0:05:54 | |
There are twice as many stars in the galaxy as we thought? | 0:05:54 | 0:05:56 | |
That's right, yes. It's just in the bit of the Milky Way | 0:05:56 | 0:05:58 | |
that Gaia has measured. There are twice as many stars in there. | 0:05:58 | 0:06:01 | |
How has Gaia doubled...? | 0:06:01 | 0:06:02 | |
That seems surprising to me. | 0:06:02 | 0:06:04 | |
I assumed that you didn't know the position before, | 0:06:04 | 0:06:06 | |
but where have they been hiding? | 0:06:06 | 0:06:08 | |
It's just because the image quality of Gaia, | 0:06:08 | 0:06:10 | |
the fact that Gaia has such high spatial resolution. | 0:06:10 | 0:06:13 | |
Because it can see sharply? | 0:06:13 | 0:06:14 | |
Exactly, see sharply, | 0:06:14 | 0:06:16 | |
and so Gaia can tell the difference | 0:06:16 | 0:06:17 | |
between two or three stars that are very close together, | 0:06:17 | 0:06:20 | |
but, nevertheless, are separate stars, | 0:06:20 | 0:06:22 | |
whereas, previously, from our images from the ground, | 0:06:22 | 0:06:25 | |
blurry sort of things, | 0:06:25 | 0:06:26 | |
this stuff here would have all been | 0:06:26 | 0:06:28 | |
merged into what we thought was one star. | 0:06:28 | 0:06:30 | |
And so, we've been looking at the map as it appears on the sky, | 0:06:30 | 0:06:33 | |
but one of the exciting things about Gaia is | 0:06:33 | 0:06:35 | |
that we have three-dimensional information as well. | 0:06:35 | 0:06:37 | |
We can go beyond this sort of two-dimensional picture. | 0:06:37 | 0:06:40 | |
Exactly, and that's the unique feature of Gaia. | 0:06:40 | 0:06:42 | |
Gaia measures distances as well as all these other things. | 0:06:42 | 0:06:45 | |
And once we get into measuring distances, | 0:06:45 | 0:06:47 | |
then we can measure the three-dimensional structure | 0:06:47 | 0:06:50 | |
of our Milky Way. | 0:06:50 | 0:06:51 | |
So far, we've only just had a taster of that, | 0:06:51 | 0:06:54 | |
so Gaia's just released two million accurate distances. | 0:06:54 | 0:06:58 | |
And so, here is the beginnings of a picture in three dimensions. | 0:06:58 | 0:07:01 | |
This is our sun, and we are about to go and see | 0:07:01 | 0:07:04 | |
the Hyades and the Pleiades cluster. | 0:07:04 | 0:07:06 | |
Both part of the autumn sky. | 0:07:06 | 0:07:08 | |
Oh, look. | 0:07:08 | 0:07:09 | |
There's Betelgeuse and the Hyades there | 0:07:09 | 0:07:11 | |
with Aldebaran in front of them. | 0:07:11 | 0:07:13 | |
The Pleiades in the corner. | 0:07:13 | 0:07:14 | |
There goes Aldebaran. It's closer to us. | 0:07:14 | 0:07:16 | |
And so, here we are, for the first time ever, | 0:07:16 | 0:07:18 | |
seeing a star cluster in three dimensions. | 0:07:18 | 0:07:21 | |
So we can tell the difference | 0:07:21 | 0:07:23 | |
between the front side and the back side of the Hyades. | 0:07:23 | 0:07:27 | |
So we know exactly in 3-D where all these stars are. | 0:07:27 | 0:07:29 | |
And this helps understand the cluster. | 0:07:29 | 0:07:31 | |
We know more about it than we did before we had this map. | 0:07:31 | 0:07:33 | |
And so, we have already discovered | 0:07:33 | 0:07:35 | |
not only how deep the Hyades cluster itself is, | 0:07:35 | 0:07:38 | |
but, actually, it's about twice as big. | 0:07:38 | 0:07:39 | |
It's amazing. What other features should we look for in this 3-D map? | 0:07:39 | 0:07:43 | |
So this dramatic Hyades example, | 0:07:43 | 0:07:45 | |
one very nearby cluster, is just a taster for what's going on. | 0:07:45 | 0:07:49 | |
We've got good distances now for just two million stars. | 0:07:49 | 0:07:53 | |
We are going to have one billion at least, | 0:07:53 | 0:07:56 | |
that will give us a three-dimensional map | 0:07:56 | 0:07:58 | |
of half of our Milky Way. | 0:07:58 | 0:08:00 | |
But, even more interestingly, | 0:08:00 | 0:08:02 | |
because Gaia's continuing to observe over time, | 0:08:02 | 0:08:05 | |
it's telling us how everything's moving, | 0:08:05 | 0:08:07 | |
and that combination of where things are | 0:08:07 | 0:08:09 | |
and how they are moving | 0:08:09 | 0:08:10 | |
allows us to determine how the galaxy works as a machine, | 0:08:10 | 0:08:14 | |
how the Milky Way actually functions, what is a spiral arm, | 0:08:14 | 0:08:17 | |
where is the dark matter and how it's evolving. | 0:08:17 | 0:08:19 | |
Well, it's going to be very exciting. | 0:08:19 | 0:08:21 | |
It's going to be fantastic. | 0:08:21 | 0:08:23 | |
So now we have a map of over a billion stars in our galactic guide, | 0:08:23 | 0:08:27 | |
but the question is, where do we go and visit? | 0:08:27 | 0:08:30 | |
What are the most interesting and exciting stars within our galaxy? | 0:08:30 | 0:08:33 | |
We invited astrophysicist Neil deGrasse Tyson, | 0:08:33 | 0:08:36 | |
who has written about this very subject | 0:08:36 | 0:08:39 | |
in his book, Welcome To The Universe, | 0:08:39 | 0:08:41 | |
to give us a guide | 0:08:41 | 0:08:43 | |
to the weird and wonderful stars of the Milky Way. | 0:08:43 | 0:08:45 | |
The sun. | 0:08:46 | 0:08:48 | |
It's a million times bigger than the Earth. | 0:08:48 | 0:08:51 | |
It's widely regarded as a yellow orb in the sky, but it's actually white. | 0:08:52 | 0:08:56 | |
You know, our sun is not the hottest | 0:08:57 | 0:08:59 | |
or the coolest or the biggest or the smallest. | 0:08:59 | 0:09:02 | |
There's nothing to distinguish it | 0:09:02 | 0:09:05 | |
among the hundreds of billions of other stars in the galaxy. | 0:09:05 | 0:09:09 | |
In fact, if you were an intergalactic alien, | 0:09:09 | 0:09:11 | |
and you came upon the Milky Way, | 0:09:11 | 0:09:13 | |
there'd be nothing about our star system | 0:09:13 | 0:09:15 | |
that would attract your attention. | 0:09:15 | 0:09:18 | |
But there's plenty of other stars in our galaxy worth a look, | 0:09:18 | 0:09:22 | |
and I've made a personal list of the top five. | 0:09:22 | 0:09:25 | |
Coming in at number five | 0:09:26 | 0:09:27 | |
of our exotic star countdown of the Milky Way | 0:09:27 | 0:09:30 | |
is SAO 206462, previously thought to just be an ordinary star. | 0:09:30 | 0:09:36 | |
When you go in and look close, | 0:09:36 | 0:09:38 | |
and you blot away the light of this relatively new star | 0:09:38 | 0:09:42 | |
that was just formed, | 0:09:42 | 0:09:43 | |
you get to see this remarkable spiral structure. | 0:09:43 | 0:09:47 | |
We are pretty confident that this is a disc of debris | 0:09:47 | 0:09:51 | |
in the act of forming brand-new planets | 0:09:51 | 0:09:55 | |
around this relatively newly born star. | 0:09:55 | 0:09:58 | |
Each of these spiral arms will likely coalesce, | 0:09:58 | 0:10:03 | |
and, in the not so distant future, | 0:10:03 | 0:10:05 | |
become single planets, one for each arm, | 0:10:05 | 0:10:08 | |
in mutual orbit around the host star. | 0:10:08 | 0:10:11 | |
We've seen discs of material before, around newborn stars, | 0:10:11 | 0:10:15 | |
hinting that planets are soon to form. | 0:10:15 | 0:10:18 | |
But this is the first time we've ever seen spiral structure. | 0:10:18 | 0:10:22 | |
This star is just at the beginning of its life, | 0:10:24 | 0:10:26 | |
and who knows what other strange phenomena | 0:10:26 | 0:10:29 | |
it will treat us to as it evolves. | 0:10:29 | 0:10:32 | |
But strange behaviour isn't the preserve of the young. | 0:10:32 | 0:10:36 | |
Coming in at number four | 0:10:36 | 0:10:37 | |
among the top five weirdest stars in the Milky Way galaxy | 0:10:37 | 0:10:42 | |
is Omicron Ceti, | 0:10:42 | 0:10:44 | |
Ceti referencing the constellation Cetus, the whale. | 0:10:44 | 0:10:48 | |
Here it is. It happens to be a red giant star. | 0:10:48 | 0:10:52 | |
Plenty of these in the galaxy, | 0:10:52 | 0:10:54 | |
not even distinguished for how it looks in visible light. | 0:10:54 | 0:10:58 | |
But if you, instead, observe this star using ultraviolet... | 0:10:58 | 0:11:02 | |
..this is what you find. | 0:11:03 | 0:11:05 | |
The star is up here... | 0:11:05 | 0:11:06 | |
..and there's this long, 13 light-year plume left behind. | 0:11:08 | 0:11:13 | |
And right up front, we have a bow shock, | 0:11:16 | 0:11:19 | |
which is evidence that this thing is ploughing through the galaxy | 0:11:19 | 0:11:23 | |
between the stars at incredible speeds. | 0:11:23 | 0:11:26 | |
In fact, we can measure it at 300,000 miles an hour. | 0:11:26 | 0:11:30 | |
We happen to know that red giants | 0:11:31 | 0:11:33 | |
only have a tenuous connection to their outer gaseous shells, | 0:11:33 | 0:11:37 | |
so going that fast, | 0:11:37 | 0:11:39 | |
it's going to lose some of that outer shell, | 0:11:39 | 0:11:42 | |
leaving it behind as it punches its way | 0:11:42 | 0:11:46 | |
through the gas of the interstellar medium. | 0:11:46 | 0:11:48 | |
We've never seen anything like this. | 0:11:48 | 0:11:50 | |
But the most spectacular sights to be seen don't just involve one star. | 0:11:52 | 0:11:57 | |
Coming in at number three is MY Camelopardalis. | 0:11:59 | 0:12:03 | |
It's not one star, it's two. | 0:12:03 | 0:12:05 | |
Two supermassive, hot blue stars | 0:12:07 | 0:12:12 | |
in orbit around one another. | 0:12:12 | 0:12:14 | |
That alone is not odd. | 0:12:14 | 0:12:16 | |
More than half the stars you see in the night sky, | 0:12:16 | 0:12:18 | |
if you pull a telescope out on them, | 0:12:18 | 0:12:20 | |
what you'll notice is that it's a double or multiple star system. | 0:12:20 | 0:12:24 | |
So, we're cool with that. | 0:12:24 | 0:12:27 | |
What's different here is that these two stars | 0:12:27 | 0:12:30 | |
are in CONTACT with one another. | 0:12:30 | 0:12:32 | |
We are fairly certain that, given enough time, | 0:12:32 | 0:12:36 | |
these two stars will completely coalesce, | 0:12:36 | 0:12:39 | |
joining their fuel supplies into one coherent star. | 0:12:39 | 0:12:43 | |
What we don't know is will that star be stable... | 0:12:44 | 0:12:47 | |
..and just join the ranks of other high-mass stars that are out there, | 0:12:48 | 0:12:52 | |
or will it be unstable and blow itself apart? | 0:12:52 | 0:12:56 | |
We don't know. | 0:12:56 | 0:12:58 | |
Just keep watching this space. | 0:12:58 | 0:13:00 | |
This isn't the only strange binary system to be seen. | 0:13:02 | 0:13:06 | |
We're down to number two. | 0:13:06 | 0:13:08 | |
That distinction goes to Gaia 14aae. | 0:13:08 | 0:13:13 | |
Once again, it's not a single star, it's a binary star system. | 0:13:13 | 0:13:17 | |
In this case, one of them is a white dwarf, | 0:13:17 | 0:13:20 | |
the end stage of a medium-mass star such as the sun, | 0:13:20 | 0:13:23 | |
and a companion star, | 0:13:23 | 0:13:25 | |
which happens to be going through its giant phase. | 0:13:25 | 0:13:29 | |
This white dwarf is effectively flaying | 0:13:29 | 0:13:32 | |
the outer layers of this giant, | 0:13:32 | 0:13:34 | |
consuming it, body and soul. | 0:13:34 | 0:13:37 | |
It's basically a stellar cannibal. | 0:13:38 | 0:13:40 | |
If the growing mass of the white dwarf crosses a certain threshold... | 0:13:42 | 0:13:46 | |
..the white dwarf will go unstable and explode, become a supernova. | 0:13:47 | 0:13:52 | |
But this isn't even the weirdest thing that can happen | 0:13:53 | 0:13:56 | |
when stars collide. | 0:13:56 | 0:13:57 | |
And now, the number one weirdest star in the Milky Way galaxy. | 0:13:59 | 0:14:04 | |
It goes by the name of V Hydrae. | 0:14:04 | 0:14:06 | |
This star, a red giant star, | 0:14:08 | 0:14:10 | |
would not otherwise call attention to itself, | 0:14:10 | 0:14:14 | |
were it not for, every eight and a half years, | 0:14:14 | 0:14:18 | |
blobs of nearly 10,000-degree plasma comes spewing out | 0:14:18 | 0:14:24 | |
at a half a million miles an hour. | 0:14:24 | 0:14:27 | |
Then it stops. | 0:14:27 | 0:14:28 | |
Eight and a half years later, it repeats. | 0:14:28 | 0:14:31 | |
Who ordered that? | 0:14:33 | 0:14:34 | |
Our best hypothesis is that this red giant star has a companion... | 0:14:35 | 0:14:40 | |
..another star in orbit around it that has a highly elliptical orbit, | 0:14:42 | 0:14:48 | |
a highly elongated orbit. | 0:14:48 | 0:14:50 | |
Spends a lot of time out far away, but when it comes in close, | 0:14:50 | 0:14:54 | |
it comes in real close and punches through | 0:14:54 | 0:14:57 | |
the physical body of the red giant itself, | 0:14:57 | 0:15:00 | |
pops out the other side. | 0:15:00 | 0:15:02 | |
We think that interaction of a hot star and the red giant | 0:15:02 | 0:15:06 | |
is what's responsible for spewing forth | 0:15:06 | 0:15:09 | |
these blobs of plasma right on schedule... | 0:15:09 | 0:15:13 | |
..every eight and a half years. | 0:15:14 | 0:15:15 | |
So, we've never seen this phenomenon before. | 0:15:17 | 0:15:21 | |
We THINK we have the right explanation for it, | 0:15:21 | 0:15:25 | |
but it remains a unique object | 0:15:25 | 0:15:27 | |
in all the star catalogues that we've accumulated. | 0:15:27 | 0:15:31 | |
And for that reason, | 0:15:31 | 0:15:33 | |
it is the weirdest star in the Milky Way. | 0:15:33 | 0:15:36 | |
And if you want to see some of Neil's top five stars for yourself, | 0:15:39 | 0:15:42 | |
Peter's here to show you how to find them. | 0:15:42 | 0:15:45 | |
When you look up at the night sky, | 0:15:49 | 0:15:50 | |
all of the stars you can see individually | 0:15:50 | 0:15:52 | |
belong to our own Milky Way galaxy. | 0:15:52 | 0:15:55 | |
Now, in the winter time, the dense part of the Milky Way, | 0:15:55 | 0:15:58 | |
which is towards the core, isn't visible. | 0:15:58 | 0:16:01 | |
But, when we look up at the sky in the winter time, | 0:16:01 | 0:16:04 | |
we're looking outward in the opposite direction. | 0:16:04 | 0:16:07 | |
This is also a great time to look for some of the five | 0:16:07 | 0:16:11 | |
must-see stars in the sky. | 0:16:11 | 0:16:13 | |
Now, I'm going to start with Omicron Ceti, | 0:16:13 | 0:16:16 | |
which is in the constellation of Cetus, the whale, or sea monster. | 0:16:16 | 0:16:20 | |
This is the comet-like star, | 0:16:20 | 0:16:22 | |
which, when viewed in ultraviolet, | 0:16:22 | 0:16:25 | |
is seen leaving a tail behind it | 0:16:25 | 0:16:27 | |
as it races through the galaxy. | 0:16:27 | 0:16:28 | |
So, this is a variable star, and at its brightest, | 0:16:30 | 0:16:33 | |
it's an easy thing to see with the naked eye, but at its dimmest, | 0:16:33 | 0:16:36 | |
as it is now, you need a telescope | 0:16:36 | 0:16:38 | |
or a pair of binoculars to pick it out. | 0:16:38 | 0:16:41 | |
Now, I'm going to use my camera | 0:16:41 | 0:16:43 | |
and see if I can take a photograph of the star. | 0:16:43 | 0:16:47 | |
To find it, first identify the Great Square of Pegasus | 0:16:48 | 0:16:52 | |
and then, below, and to the left, | 0:16:52 | 0:16:54 | |
find the faint V-shaped string of stars of Pisces. | 0:16:54 | 0:16:58 | |
The string comes to a sharp point at the star Alrescha | 0:16:58 | 0:17:02 | |
and this acts like an arrow | 0:17:02 | 0:17:03 | |
pointing directly to Omicron Ceti, also called Mira. | 0:17:03 | 0:17:07 | |
I'm actually finding it quite tricky to locate the field where Mira is | 0:17:11 | 0:17:15 | |
at the moment, and the reason for that is | 0:17:15 | 0:17:17 | |
that there is a full moon coming up | 0:17:17 | 0:17:19 | |
and that's making the sky really bright | 0:17:19 | 0:17:21 | |
and drowning out all the faint stars. | 0:17:21 | 0:17:23 | |
But I think I'm more or less in the right area now. | 0:17:23 | 0:17:26 | |
And I think I've got it. | 0:17:27 | 0:17:28 | |
There are two stars very close to one another. | 0:17:28 | 0:17:31 | |
One of them is red, and that is Omicron Ceti, | 0:17:31 | 0:17:34 | |
or Mira as it's known, and it's red because it's a red giant star. | 0:17:34 | 0:17:39 | |
Now, I can't see the tail | 0:17:39 | 0:17:41 | |
because that's visible in UV light and UV light | 0:17:41 | 0:17:43 | |
is blocked by the atmosphere, | 0:17:43 | 0:17:45 | |
so that's best left to the space telescopes, | 0:17:45 | 0:17:47 | |
but I've definitely got it, so I'm happy. | 0:17:47 | 0:17:50 | |
And in the faint constellation of Camelopardalis, | 0:17:54 | 0:17:56 | |
which lies to the north of Auriga and Perseus, | 0:17:56 | 0:17:59 | |
is the merging binary star, MY Camelopardalis. | 0:17:59 | 0:18:04 | |
Now, this is so far north in the sky | 0:18:04 | 0:18:06 | |
that from the United Kingdom it never sets, | 0:18:06 | 0:18:08 | |
but you will need a telescope to see it. | 0:18:08 | 0:18:11 | |
The best way to find it is to extend a line | 0:18:11 | 0:18:14 | |
from the famous eclipsing binary star, Algol, through Mirfak, | 0:18:14 | 0:18:18 | |
the two brightest stars in the constellation of Perseus. | 0:18:18 | 0:18:22 | |
Extend the line they make north for the same distance again, | 0:18:22 | 0:18:25 | |
and you'll be in the right area. | 0:18:25 | 0:18:27 | |
And if you're willing to stay up until the early hours, | 0:18:28 | 0:18:31 | |
then you stand a chance of seeing | 0:18:31 | 0:18:33 | |
the number one strangest star in the galaxy, V Hydrae, | 0:18:33 | 0:18:37 | |
the star system emitting the plasma balls. | 0:18:37 | 0:18:40 | |
It lies in the belly of Hydra, the water snake. | 0:18:42 | 0:18:45 | |
Halfway along the snake, find new Hydrae and 5 degrees below that, | 0:18:45 | 0:18:50 | |
at the bottom of a Y-shaped pattern of stars, is V Hydrae. | 0:18:50 | 0:18:53 | |
A telescope is the best way to see it. | 0:18:54 | 0:18:56 | |
But sadly, the last two of Neil's favourite stars | 0:18:59 | 0:19:02 | |
are too tricky to see. | 0:19:02 | 0:19:04 | |
SAO 206462, the star with the spiral arms, | 0:19:05 | 0:19:10 | |
is too far south to be seen from the UK. | 0:19:10 | 0:19:13 | |
And Gaia 14aae, the cannibal binary system, is extremely faint, | 0:19:13 | 0:19:19 | |
so it would be very hard to spot without a large telescope. | 0:19:19 | 0:19:22 | |
This time of year is also great | 0:19:26 | 0:19:28 | |
for seeing another of the stellar highlights | 0:19:28 | 0:19:30 | |
featured earlier, the Hyades star cluster, | 0:19:30 | 0:19:34 | |
which Gaia has mapped in 3-D | 0:19:34 | 0:19:36 | |
and which can even be seen with the naked eye. | 0:19:36 | 0:19:38 | |
But the best way to see them | 0:19:40 | 0:19:42 | |
is to use a pair of binoculars or a telescope | 0:19:42 | 0:19:45 | |
and if you use such an instrument, | 0:19:45 | 0:19:47 | |
you'll see them in far greater detail. | 0:19:47 | 0:19:49 | |
Now I'm going to take a photograph to see what I can get. | 0:19:49 | 0:19:53 | |
The easiest way to find the Hyades | 0:19:53 | 0:19:55 | |
is to extend the line made by Orion's Belt | 0:19:55 | 0:19:58 | |
up to the north west, or up and right as seen from the UK, | 0:19:58 | 0:20:03 | |
until you arrive at the bright orange star, Aldebaran, | 0:20:03 | 0:20:06 | |
which is part of the V-shaped face of Taurus the bull. | 0:20:06 | 0:20:09 | |
So, the face of Taurus the bull is the Hyades | 0:20:12 | 0:20:15 | |
and the Hyades are about 625 million years old, | 0:20:15 | 0:20:19 | |
so they're getting to the end of their life, | 0:20:19 | 0:20:21 | |
so there are lots of red giants and white dwarfs in this cluster. | 0:20:21 | 0:20:25 | |
Our understanding of the Milky Way is improving all the time. | 0:20:30 | 0:20:33 | |
Not only do we now have Gaia's billion-star map, | 0:20:35 | 0:20:38 | |
but recently, ground-based telescopes | 0:20:39 | 0:20:41 | |
have created the most comprehensive map ever made | 0:20:41 | 0:20:44 | |
of the distribution of dust in the galaxy. | 0:20:44 | 0:20:47 | |
It shows the spiral arms, star-forming regions | 0:20:49 | 0:20:52 | |
and streams of dust. | 0:20:52 | 0:20:53 | |
But beyond the stars and dust, | 0:20:56 | 0:20:57 | |
there are other parts of the galaxy | 0:20:57 | 0:20:59 | |
that we still know extremely little about. | 0:20:59 | 0:21:02 | |
The final part of our Guide To The Galaxy | 0:21:04 | 0:21:06 | |
takes us to one of the Milky Way's | 0:21:06 | 0:21:07 | |
most mysterious and interesting regions - its outer reaches. | 0:21:07 | 0:21:11 | |
It's long been thought that the visible disc of the galaxy | 0:21:11 | 0:21:14 | |
is embedded in a huge corona, | 0:21:14 | 0:21:17 | |
a vast cloud of hot, ionised gas. | 0:21:17 | 0:21:20 | |
And if it's there, it might help us solve a problem, | 0:21:20 | 0:21:24 | |
because when you add up all the dust, | 0:21:24 | 0:21:25 | |
all the gas and all the stars in the disc, all the normal matter, | 0:21:25 | 0:21:29 | |
you find there's only about half as much as there should be, | 0:21:29 | 0:21:33 | |
and it may be that that missing mass is hiding in the corona. | 0:21:33 | 0:21:37 | |
Well, we know very little about this strange, enigmatic region | 0:21:37 | 0:21:41 | |
but scientists here have made a new discovery. | 0:21:41 | 0:21:44 | |
Maggie went to meet Denis Erkal | 0:21:46 | 0:21:48 | |
to find out what this discovery can tell us | 0:21:48 | 0:21:51 | |
about the nature of the corona | 0:21:51 | 0:21:52 | |
and the missing matter in our galaxy. | 0:21:52 | 0:21:54 | |
So, Denis, thank you for coming up to speak to us | 0:21:56 | 0:21:58 | |
and this is a glorious picture. | 0:21:58 | 0:22:00 | |
What are we seeing here? | 0:22:00 | 0:22:01 | |
This is a picture that I took in Chile, | 0:22:01 | 0:22:03 | |
so this is the night sky as seen from Chile, | 0:22:03 | 0:22:05 | |
so this is the Milky Way right here, | 0:22:05 | 0:22:07 | |
this is the disc of the Milky Way, | 0:22:07 | 0:22:08 | |
and these are the objects we are interested in. | 0:22:08 | 0:22:10 | |
This is the small and large Magellanic Cloud. | 0:22:10 | 0:22:12 | |
These are two dwarf galaxies | 0:22:12 | 0:22:14 | |
that, very recently, they had their closest approach to the Milky Way. | 0:22:14 | 0:22:16 | |
These can only be seen from the southern hemisphere. | 0:22:16 | 0:22:19 | |
These can only be seen from relatively far south. | 0:22:19 | 0:22:21 | |
So, what have you discovered so far? | 0:22:21 | 0:22:23 | |
So, let's just zoom in a little bit. | 0:22:23 | 0:22:24 | |
So, this is another picture of the large Magellanic Cloud | 0:22:24 | 0:22:27 | |
and the small Magellanic Cloud. | 0:22:27 | 0:22:29 | |
This was the optical image, but we can also show what happens | 0:22:29 | 0:22:31 | |
when we overlay data from a radio telescope. | 0:22:31 | 0:22:34 | |
So, this shows hydrogen | 0:22:34 | 0:22:35 | |
around the large and the small Magellanic Cloud. | 0:22:35 | 0:22:38 | |
What we believe happened was about a few hundred million years ago, | 0:22:38 | 0:22:40 | |
the small Magellanic Cloud | 0:22:40 | 0:22:42 | |
passed near the large Magellanic Cloud, | 0:22:42 | 0:22:44 | |
and as it passed nearby, | 0:22:44 | 0:22:45 | |
the gravitational force from the large Magellanic Cloud | 0:22:45 | 0:22:48 | |
shredded part of the small Magellanic Cloud, | 0:22:48 | 0:22:50 | |
ripping off this gas bridge. | 0:22:50 | 0:22:52 | |
-Oh, wow. -And so now we can overlay this blue line, | 0:22:52 | 0:22:56 | |
which just shows us the densest part of the gas. | 0:22:56 | 0:22:59 | |
So, we've known about this gas bridge for a long time, | 0:22:59 | 0:23:02 | |
but what we found recently was a stellar bridge. | 0:23:02 | 0:23:04 | |
And so this shows the data from the Gaia satellite. | 0:23:04 | 0:23:08 | |
So here, the background image is the one I showed you before, | 0:23:08 | 0:23:11 | |
and in white, this milky cloud, | 0:23:11 | 0:23:13 | |
shows the stars from Gaia smoothed over | 0:23:13 | 0:23:15 | |
to make an artist's impression of the data. | 0:23:15 | 0:23:17 | |
OK, so Gaia has discovered these stars and it looks like, yeah, | 0:23:17 | 0:23:20 | |
there's a stellar bridge, a bridge of stars. | 0:23:20 | 0:23:22 | |
That's right, so this is the stellar bridge coming down here, | 0:23:22 | 0:23:25 | |
so just like the gas was ripped off from the small Magellanic Cloud, | 0:23:25 | 0:23:28 | |
we think, at the same time, stars were ripped off. | 0:23:28 | 0:23:31 | |
So the gas and star bridge were created at the same time and place. | 0:23:32 | 0:23:37 | |
But there's a mystery, because today, when the images are overlaid, | 0:23:37 | 0:23:41 | |
you can see that the two bridges are no longer aligned. | 0:23:41 | 0:23:44 | |
And Denis believes the explanation for this discrepancy is the corona. | 0:23:44 | 0:23:50 | |
So, the large and small Magellanic Cloud | 0:23:50 | 0:23:51 | |
are both moving down roughly in this direction, | 0:23:51 | 0:23:54 | |
so we think, as they move through the corona, | 0:23:54 | 0:23:56 | |
what happens is the gas gets pushed back | 0:23:56 | 0:23:58 | |
by the corona from the Milky Way. | 0:23:58 | 0:24:00 | |
The stars also feel that pressure from the corona, | 0:24:00 | 0:24:02 | |
but since they're small and dense, | 0:24:02 | 0:24:04 | |
they basically punch through the corona, | 0:24:04 | 0:24:05 | |
so they don't get pushed back at all. | 0:24:05 | 0:24:07 | |
So, this result is really good evidence | 0:24:07 | 0:24:09 | |
that the corona actually exists. | 0:24:09 | 0:24:11 | |
That's right, there was some evidence before, | 0:24:11 | 0:24:12 | |
but we think this adds even stronger evidence, | 0:24:12 | 0:24:14 | |
so we're very convinced that the corona is there. | 0:24:14 | 0:24:16 | |
How far does it extend from our galaxy? | 0:24:16 | 0:24:18 | |
We think it extends out to at least 600,000 light years | 0:24:18 | 0:24:20 | |
from the centre of our galaxy. | 0:24:20 | 0:24:22 | |
Wow, but that's sort of well on its way to Andromeda, isn't it? | 0:24:22 | 0:24:24 | |
That's right, that's about a third of the way to Andromeda, | 0:24:24 | 0:24:27 | |
so it's really far out. | 0:24:27 | 0:24:28 | |
-Wow. -It goes at least that far, we think. | 0:24:28 | 0:24:29 | |
So, with this massive corona around our galaxy, | 0:24:29 | 0:24:32 | |
can that help account for the missing visible matter | 0:24:32 | 0:24:34 | |
in our galaxy? | 0:24:34 | 0:24:35 | |
Yes, we think that this corona can account for | 0:24:35 | 0:24:37 | |
a significant fraction of | 0:24:37 | 0:24:39 | |
the missing normal matter around our galaxy. | 0:24:39 | 0:24:41 | |
Wow. That's quite a result, isn't it? | 0:24:41 | 0:24:43 | |
Yeah, it's pretty exciting. | 0:24:43 | 0:24:44 | |
There's another layer of significance to this finding, | 0:24:44 | 0:24:48 | |
because there's evidence of a similar corona of hot gas | 0:24:48 | 0:24:51 | |
around our neighbouring galaxy, Andromeda. | 0:24:51 | 0:24:54 | |
Andromeda is about 2.5 million light years away, | 0:24:55 | 0:24:58 | |
but it's on a collision course with the Milky Way. | 0:24:58 | 0:25:02 | |
We've measured that Andromeda has a corona, | 0:25:02 | 0:25:04 | |
and it extends halfway to our galaxy, | 0:25:04 | 0:25:06 | |
and now we're getting this strong evidence | 0:25:06 | 0:25:08 | |
that we've got a corona that extends a long way. | 0:25:08 | 0:25:10 | |
Is there a possibility they could be touching? | 0:25:10 | 0:25:12 | |
That's right, it is very possible. | 0:25:12 | 0:25:14 | |
From our models, we think it's very likely | 0:25:14 | 0:25:16 | |
that the very outer extents of our galaxy | 0:25:16 | 0:25:18 | |
and Andromeda are touching right now. | 0:25:18 | 0:25:21 | |
So, I've often heard it quoted that in, you know, four, | 0:25:21 | 0:25:23 | |
five billion years' time, | 0:25:23 | 0:25:25 | |
the Milky Way and Andromeda will collide, | 0:25:25 | 0:25:27 | |
but it sounds as if the collision's already begun. | 0:25:27 | 0:25:30 | |
In a way it has, yes, but these are just the very outer, | 0:25:30 | 0:25:32 | |
tenuous edges of the coronas of the Milky Way and Andromeda, but, yes, | 0:25:32 | 0:25:35 | |
the collision is starting to start now. | 0:25:35 | 0:25:37 | |
Well, I think that's pretty exciting. | 0:25:37 | 0:25:39 | |
Thank you so much for coming in and talking to us. | 0:25:39 | 0:25:41 | |
-Thanks, it's been a pleasure. Thank you. -Thank you. | 0:25:41 | 0:25:43 | |
The collision of the Milky Way and Andromeda | 0:25:46 | 0:25:48 | |
will eventually create a new, giant galaxy. | 0:25:48 | 0:25:51 | |
It's extraordinary to think that the first contact | 0:25:52 | 0:25:55 | |
between the two galaxies may have already begun, | 0:25:55 | 0:25:58 | |
but it'll be another four billion years or so | 0:25:58 | 0:26:01 | |
before the merger is complete. | 0:26:01 | 0:26:02 | |
It turns out that this intergalactic collision | 0:26:04 | 0:26:07 | |
will not be a new experience for the Milky Way... | 0:26:07 | 0:26:09 | |
..because Gaia has revealed | 0:26:10 | 0:26:12 | |
that our galaxy is the product of many previous | 0:26:12 | 0:26:14 | |
smaller galactic mergers. | 0:26:14 | 0:26:17 | |
The main disc of the galaxy | 0:26:17 | 0:26:19 | |
is surrounded by a halo of stars and clusters, | 0:26:19 | 0:26:22 | |
which live both above and below the disc, like this. | 0:26:22 | 0:26:25 | |
But what's new is that, thanks to Gaia, | 0:26:25 | 0:26:28 | |
we can work out how this whole system is moving. | 0:26:28 | 0:26:31 | |
Now, the disc is rotating, we've known that for a long while, | 0:26:31 | 0:26:34 | |
so it's spinning in this sort of direction. | 0:26:34 | 0:26:37 | |
But what Gaia has found is that some of these clusters | 0:26:37 | 0:26:40 | |
are moving through the disc | 0:26:40 | 0:26:41 | |
and they're doing so in the opposite direction | 0:26:41 | 0:26:45 | |
to the rotation of the disc itself, and so what that means is | 0:26:45 | 0:26:48 | |
that these clusters are the remnants of galaxies, | 0:26:48 | 0:26:51 | |
which our Milky Way has accreted. | 0:26:51 | 0:26:53 | |
Our galaxy is growing through galactic cannibalism. | 0:26:53 | 0:26:57 | |
And this process is still going on. | 0:26:57 | 0:26:59 | |
The Magellanic Clouds Denis was talking to Maggie about earlier | 0:26:59 | 0:27:02 | |
will almost certainly be eaten in the next few hundred million years. | 0:27:02 | 0:27:05 | |
That's it for now from our Guide To The Galaxy. | 0:27:07 | 0:27:09 | |
But don't forget, our understanding of the Milky Way | 0:27:09 | 0:27:12 | |
is undergoing a revolution, | 0:27:12 | 0:27:14 | |
so tune in in a year or so's time, | 0:27:14 | 0:27:16 | |
when we get the next batch of data from Gaia. | 0:27:16 | 0:27:19 | |
Next month we have a special programme. | 0:27:19 | 0:27:22 | |
We'll be taking over some of the telescopes | 0:27:22 | 0:27:24 | |
under the clear skies of La Palma in the Canary Islands. | 0:27:24 | 0:27:27 | |
And we want you to tell us what we should point the telescopes at. | 0:27:27 | 0:27:32 | |
Find out more on our website | 0:27:32 | 0:27:34 | |
and then e-mail or tweet your suggestions | 0:27:34 | 0:27:36 | |
to the usual addresses on the screen now. | 0:27:36 | 0:27:38 | |
And don't forget you can already check out | 0:27:41 | 0:27:43 | |
our star guide on the website. | 0:27:43 | 0:27:45 | |
In the meantime, get outside | 0:27:45 | 0:27:46 | |
-and get looking up. -Good night. | 0:27:46 | 0:27:49 |