a colossal Never-Before-Spotted structure found in the milky way
Imagine you are swimming in a large pool and you want to calculate its volume or discerning the
locations of distant floating objects. Do you think it would be easy? Well,
bad news for you! It's all but easy.
And if the pool has the size of our galaxy, it is really really hard.
Studying morphology, i.e. the shape of our galaxy, is a difficult thing to do, and astronomers during
the centuries were puzzled by this problem. Why is that? Because we don't have
directed eyesight of our galaxy. From our position inside the Milky Way,
much of its size, contents, and three-dimensional structure is really tricky to figure out.
There's a lot that eludes us or is impossible to calculate.
What we currently know is that we live in a spiral galaxy.
It’s called a spiral galaxy because if you could view it from the top or bottom,
it would look like a spinning pinwheel. The Sun is located on one of the spiral arms,
about 25,000 light-years away from the centre of the galaxy.
Even if you could travel at the speed of light - 300,000 kilometres, or 186,000 miles,
per second -, it would take you about 25,000 years to reach the middle of the Milky Way.
All of this is pretty well known to the scientific community. But
then a discovery comes along that makes you wonder, how in the heck did we miss that?!
Follow me in this video to get to know more about our fantastic galaxy and its new...Cattail!
Astronomers discovered a new structure, and named it “Cattail”.
But it is such a wonder. Before seeing what we know about it,
let's talk a bit about the structure of our galaxy:
it will help us understand better why this discovery is so peculiar.
The Milky Way Galaxy’s structure is fairly typical of a large spiral system. This structure
can be viewed as consisting of six separate parts: (1) a nucleus, (2) a central bulge,
(3) a disk (both a thin and a thick disk), (4) spiral arms, (5) a spherical component,
and (6) a massive halo. Some of these components blend into each other.
At the very centre of the Galaxy lies a remarkable object—a
massive black hole surrounded by an accretion disk of high-temperature gas.
Surrounding the nucleus is an extended bulge of stars that is nearly spherical
in shape and that consists primarily of Population II stars, i.e. old red stars.
But the most interesting part is maybe the disk. It extends from the nucleus out to
approximately 75,000 light-years. The disk can be thought of as being the
underlying body of stars upon which the arms are superimposed. This body has a thickness that is
roughly one-fifth its diameter, but different components have different characteristic
thicknesses. The thinnest component, often called the "thin disk," includes the dust and gas and the
youngest stars, while a thicker component, the "thick disk,” includes somewhat older stars.
Astronomers noticed a warp in the disk of the Milky Way, and they now think it was the result
of a “recent” interaction with another galaxy. “Recent” means that roughly three billion years
ago, the scientists suggest, a satellite galaxy came close enough to our own
to create a ripple effect still visible in the Milky Way's stars today.
Finally, we would like to say something about spiral arms.
Astronomers did not know that the Galaxy had a spiral structure
until 1953 when the distances to stellar associations were first obtained reliably.
This structure is easier to discern from radio maps of either
neutral hydrogen or molecular clouds since both can be detected through the dust of the galaxy.
The Cattail, indeed, is a hydrogen cloud.
This information will be useful for our understanding of the discovery.
Here's what we know about the Cattail: 1) It's a curl of gas.
It's a curl of gas and it is so large astronomers are not even sure whether or not
it might be part of a galactic spiral arm that we never noticed...until now.
2) It's the largest filament of gas in our Galaxy
This new-discovered curl of gas, the Cattail, may be the largest filament
of gas in our galaxy discovered to date! You can read this on the Astrophysical Journal Letters.
The discovery team, from Nanjing University in China,
says it "appears to be so far the furthest and largest giant filament in the galaxy.”
Here, instead, is what we don't know.
1) Why is it so huge.
Astronomers have no clue how such a huge filament is produced at the extreme galactic location,
and so the debate remains open. Cattail might be part of a new arm of our Milky
Way, but it is puzzling that the structure does not fully follow the warp of the galactic disk.
However, astronomers estimate its mass to be 6.5 × 10^4 solar masses.
Also, as the data suggested, it should be 3,590 light-years
in length and 675 light-years in width. But when astronomers combined the data
with the HI4PI all-sky HI survey, they found that the Cattail could
be even longer: as long as 16,300 light-years. That would make it even more colossal than the
gas structure known as Gould's Belt, which was recently found to be 9,000 light-years long.
2) Why we didn't notice it before.
Mapping the Milky Way in three dimensions it's a hard job.
We barely know how to do that!
One reason for this is that it's very tricky to work out the distances to cosmic objects.
Another is that there is a lot of stuff out there, so it can be hard to know if something
is a significant grouping or just a random collection spread out along a line of sight.
Let's see how this discovery was made.
As we said, the discovery was made by a team led by Nanjing University astronomer Chong Li.
They were using the huge Five-hundred-meter Aperture Spherical radio Telescope (FAST)
to look for clouds of neutral atomic hydrogen (HI).
Neutral atomic hydrogen clouds are important to us because they're found in the spiral
arms of galaxies like the Milky Way. They are actually used to map the number and arrangement
of the galaxy's arms from within, studying subtle differences in hydrogen light.
In August 2019, the researchers used FAST to look for HI radio emissions,
and the data revealed what appeared to be a large structure, the Cattail.
When they calculated how fast the structure was moving, they couldn't believe their eyes:
its velocity was consistent with a distance of around 71,750 light-years from the galactic
centre - the outer regions of the galaxy. That distance - farther than any known
spiral arms in that region of the galaxy - would mean the thing is absolutely huge.
Why is this discovery so important?
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Well, this discovery is important because the Cattail raises some interesting questions.
Usually, gas filaments occur closer to the galactic centre
and are often associated with spiral arms. And if it's a filament, it's unclear how
the Cattail could have formed and remained out beyond the known spiral arms of the Milky Way.
On the other hand, if it's a spiral arm, it is a very peculiar one.
The galactic disc of the Milky Way, as we said, is wobbly and warped from an encounter with another
galaxy, a long time ago. Yet the Cattail's shape seems not entirely conformed to this
warp - which it should be if it was a spiral arm. Of course, these peculiarities suggest that
we might want to take a closer look at this amazing structure.
"While these questions remain open with the existing data, the observations provide
new insights into our understanding of the galactic structure.", the researchers wrote.
This video ends here! Thanks for watching everyone!
What do you think about the Cattail? Does this discovery amaze you?
Let us know in the comment below! See you next time on the channel!