The Most massive stars in the universe
If you look up to the sky in the night, you'll soon realize that we are surrounded by stars.
Some of them are bright, some others are fainter. This could be because they are far away, or
maybe it's just that they are intrinsically faint.
The only way to understand it is by calculating their distance from us.
According to the spectral classification of stars, the brightest ones are the biggest
ones. Usually, smaller stars are not so bright.
But which stars are the most massive ones? Do we have a list of the most massive stars
in the universe? Thank God, the answer is yes.
In this video, we'll talk about them. Spoiler: the most massive one is more than 215 times
the mass of our Sun.
Astronomers study stars' characteristics and work to calculate their distances, their temperatures
and their masses. Why do they do so? The answer is pretty simple: they want to understand
something about how they are born, live and, eventually, die. Among these, maybe the death
of a star is the most fascinating event that could happen because a star could go black
hole, neutron star or supernova according to mass it had when it was born.
Some of the stars are only a fraction of the Sun's mass (which isn't actually a big star!).
Others are equivalent to hundreds of suns.
We said that bigger stars are usually brighter. But pay attention here, because “largest”
is not equivalent to “most massive” when it comes to stars.
From theoretical studies and models, we see that the limit to a star's mass is about 120
solar masses. What we really mean when we say that, is a
star can't remain stable if overcomes that mass limit of 120 solar masses. That's what
theory says. But the reality is always more complicated
than models. There are stars that are way beyond that limit.
We know this because we observed them. How they can exist is a problem that astronomers
are trying to solve.
R136a1 For example, the star R136a1 is 215 times
more massive than our sun. This star is incredibly heavy.
It currently holds the record as the most massive star ever known to exist in the universe.
But this is not its only record. It is also the most luminous one, at nearly 9 million
times the luminosity of our Sun. Sunglasses can do nothing against this monstrous star!
R136a1 is part of a so-called supercluster (that is, a messy region filled with stars).
You can find it in the Tarantula Nebula in the famous Large Magellanic cloud, also known
as LMC. Its temperature is about 46.000 K, maybe the
temperature of hell! The cluster can be seen in the far-southern
celestial hemisphere, so I'm sorry if you are from the northern one.
The distance to R136a1 cannot be determined directly but is assumed to be at the same
distance as the Large Magellanic Cloud at around 50 kiloparsecs.
WR101e Another star very massive that exceed 150
times the mass of our Sun is WR 101e. Unluckily we know very little about this giant
celestial object. We can say that it is a wolf rayet star. What?
You don't know what a wolf rayet star is? So you need some quick pills of star evolution
uh?
Wolf Rayet stars They are massive stars that are at an advanced
stage of stellar evolution and losing mass at a very high rate. With masses typically
greater than 25 times that of the Sun, they have brief lifetimes and are therefore quite
rare objects. We know of about 220 in our own Galaxy, but astronomers have estimated
that the Milky Way may contain between 1,000 and 2,000 such objects, the majority hidden
by dust.
Another famous star that is one of the most massive is located in the Sagittarius constellation,
and it is surrounded by the Peony Nebula. It is therefore called Peony Nebula star.
What it actually is? It is again a Wolf Rayet star. In particular,
it is a class blue hypergiant, similar to R136a1. It is 150 solar masses, and it is
also a rather large star: its radius is about 100 times that of our host star!
Could you even imagine such a huge star? Because I'm finding it hard to do so!
By the way, if you are curious, the constellation of Sagittarius hosts a lot of amazing astronomical
objects. For example, you can easily observe M24.
M24, also known as the Small Sagittarius Star Cloud, is a large naked eye expanse of stars,
clusters, nebulosity and other objects located in Sagittarius. It is visible to the naked
eye as a large detached part of the Milky Way. The object is a fantastic sight in binoculars
and small telescopes. It's claimed that M24 has the densest concentration of individual
stars visible, around a thousand, in a single binocular field of view. It should not be
confused with the nearby Large Sagittarius Star Cloud which lies about ten degrees to
the south. The Small Sagittarius Star Cloud is not a
true deep-sky object but results from a rare alignment between the Earth and the centre
of our galaxy. We would expect this region to be packed with interstellar dust, however
by chance we are looking through a gap in the dust. As a result, many thousands of distant
stars, clusters and nebulae are visible that would otherwise be obscured. Spatially, M24
covers a volume up to 16,000 light-years deep. M24 can be found 7 degrees north and a little
west of the top star of the bright teapot asterism, Kaus Borealis. Positioned north
of M24 is open cluster M18 and the Omega Nebula (M17). All three objects are visible in the
same binocular field of view. Open clusters M23 and M25 are located a few degrees west
and east of M24 respectively. M24 was discovered by Charles Messier on June
20, 1764. It's best seen from southern or equatorial latitudes during the months of
June, July and August.
Let's go on and see some other massive stars.
HD93129A The one we want to talk about now is HD 93129A.
This is a blue hypergiant (it means is veeeery hot and veeery big!) and it is likely one
of the most massive stars in the Milky Way. It is relatively close to us compared to other
stars above mentioned, and it is located in the NGC 3372 Nebula, in the constellation
Carina. The mass of this star is estimated to be around
120 to 127 solar masses. Fun fact: it is part of a binary system and
it's the heavier of the two because its companion is “only” 80 solar masses.
Talking about Carina, you can add HD93250 to the list of blue hypergiants on this list.
It has a mass of about 118 times the mass of our sun, but little else is known about
this object.
PISMIS 24-1A and B A star with a strange name is Pismis 24-1A.
It is located in the Pismis 24 open cluster, and it is a blu variable.
How do you say? You don't know what a blu variable supergiant is?
Here we are again with another astrophysical pill of stellar evolution!
The luminous blue variables (LBVs) are a recently recognized class of massive supergiants. Also
called S Dor variables, after their Large Magellanic Cloud prototype, these are the
most luminous stars in a galaxy and are easily identified in extragalactic systems. Their
amplitudes range from less than 1 magnitude to over 5. Also called Hubble–Sandage variables,
they display long (years) time scales for temperature and luminosity changes, often
ejecting shells that form pseudophotospheres, causing their spectral types to change from
O to as late as F. The galactic supergiant P Cygni, well known for its high rate of mass
loss and irregular light variations, is a galactic member of this class.
Pismis 24-1A's sister is Pismis 24-1B. As you can see, astronomers have plenty of
imagination when it comes to names! This star, like its sister, is another 100+
solar mass star in Pismis 24 region, within the constellation of Scorpius.
In this video, we've been talking a lot about the most massive stars.
But why did we do so? Why is important to study massive stars?
"Before finding out the answer to this question, be sure to like or dislike the video so that
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The answer is pretty clear if we consider the introduction to a famous paper by Robert
C. Kennicutt from Steward observatory, Arizona.
In its article on the role of massive stars in astrophysics, it is stated:
“Over the past few decades, it has become apparent that the influence of massive stars
extends well beyond the confines of their immediate stellar systems. The radiation output
from massive stars ionizes their interstellar surroundings and probably have a profound
influence on the subsequent formation of stars in their environments.[...] Massive stars
also play a profound role as the source population for neutron stars, black holes, and the diverse
set of high-energy phenomena and processes associated with those objects. Nevertheless,
it has become apparent over the last 5–10 years that the reach of massive stars is even
more profound than we had appreciated earlier. Observations from an armada of space facilities
along with deeper ground-based observations from the new generation of telescopes have
revealed the profound influence that concentrated injection of energy from stellar radiation,
winds, and supernovae can have on present-day starburst galaxies, influences that presumably
replicate those that occurred in the galaxy population as whole billions of years ago.
These “feedback” processes are now thought to be important for determining the present-day
mass and luminosity functions of galaxies, for determining the structure of low-mass
galaxies, and for enriching galaxies as well as the intergalactic medium in heavy elements.”
If you are an astronomer or an astronomy fan, I highly recommend reading this paper. You
can find it in the description! Let us know what you think about it in the comments.
"This video ends here! Thanks for watching everyone! Are you in love with stars? Did
you like this video about the most massive ones? Let us know in the comments below, be
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