What is the coldest place in the Milky Way Galaxy?

 At just one degree above absolute zero, the coldest place in the Milky Way isn't a frozen, empty void. It's a dying star violently expelling gas at 164 kilometers per second.

Known as the Boomerang Nebula, this system is located about 5,000 light-years from Earth in the constellation Centaurus. At just 1 Kelvin (−272.15 °C or −457.87 °F), it is colder than the cosmic microwave background radiation (2.7 Kelvin), the faint afterglow of the Big Bang that establishes a baseline temperature for empty space. The Boomerang Nebula is the only object ever discovered that is naturally colder than the background radiation of the universe itself.

This extreme cold is not caused by an absence of energy, but by rapid thermodynamic expansion. The Boomerang Nebula is in a brief transitional phase known as a pre-planetary nebula. Its central dying star is shedding its outer layers into space, losing mass about 100 times faster than similar objects.

When a gas expands rapidly without any heat being added, its temperature drops—a phenomenon known as adiabatic cooling. This is the exact same principle that causes a can of compressed air to turn cold in your hand when you hold the trigger. The dying star is ejecting gas so fast and expanding it so quickly that the nebula acts as a cosmic-scale refrigerator, dropping the temperature of the surrounding gas down to near absolute zero.

When astronomers first observed the object with ground-based telescopes in 1980, its slightly curved appearance led them to name it the Boomerang Nebula. However, when the Hubble Space Telescope later captured the system in high resolution, the imagery revealed that the visible gas actually forms a highly symmetric bow-tie shape. Later observations with the ALMA radio telescope demonstrated that even this visual is a partial illusion; a dense disc of dust blocks visible light around the star's equator, allowing illumination to leak out only through the two opposed lobes.

The Boomerang Nebula as photographed by the Hubble Space Telescope. Source: Wikimedia Commons.

Is it possible for humanity to leave the Milky Way Galaxy using only current technology and scientific knowledge?

 No, absolutely not!

Okay, wait maybe…

Wait again. NOOOOOOOO, it’s incredibly unlikely!

Let’s face the reality here. The edge of the Milky Way galaxy is about 25.000 light-years away. That is $2.37\cdot {10}^{17}$ kilometres. That is about 1.5 billion times the distance to our Sun. Even light needs 8,3 minutes to cover the distance to the Sun.

However, let's try to make a travel kit anyway after we realise that it probably takes more than 1 human life to get that mission done. Bring some toys.

Let's try to travel out of here:

If we travel as fast as the faster human-made object, the Voyager 2, we will have a travelling speed of about 54,000 km/h. Wooo, that's fast. Okay, it’s not actually that fast.

How long will we travel? Accounting for the fact that 25.000 light-years are equivalent to $2.37\cdot {10}^{17}km$ and the speed I mentioned above, we would only need a short time of

$t=\frac{distance}{velocity}=501,000,000$ years.

And now comes the fun part, which is why I said you might want to bring some toys. We need 501 million years to travel 25,000 light years, so we would need about 16.7 million generations if every generation is about 30 years apart.

So, bring lots of toys to your big ass space ship and you will have some babies who won't cry all the time. ;)

For a long time the Milky Way Galaxy had 100 billion stars, but the figure was changed to 400 billion stars. Why was the number of stars revised? Is there a rationale for the change?

 

For a long time the Milky Way Galaxy had 100 billion stars, but the figure was changed to 400 billion stars. Why was the number of stars revised? Is there a rationale for the change?

Certain issues that make it difficult for us to know precisely how many stars are in our galaxy also make it challenging to untangle some of its other mysteries and even resolve some enigmas of the Universe.

Our Milky Way Galaxy is currently thought to contain 100 to 400 billion stars. This is a vast spread of estimates. About 73% of suns are very faint red dwarfs, and their masses start from about 0.08 times the mass of the Sun. It's difficult to spot these and other tiny types of stars like white dwarfs and brown dwarfs and count them from considerable distances. The Milky Way is 100 000 light-years across. Many stars are part of multi-star systems that are very close together, and from a significant distance, it's difficult to tell if a dot in the sky is a single star or a binary or more.

Besides that, our galaxy contains many gas clouds and many denser regions, like clusters of stars, and many are pretty big. The central bulge of the galaxy is the most prominent such feature. We are located in a spiral disk about 1000 light-years thick, and when we look edge on from where we are, like in the image above of another galaxy, because of all these other features that block our view, we cannot see what is behind. Astronomers try to estimate the number of suns in our galaxy by counting their number near us and extending the figure that we get from our region to the galaxy as a whole. Still, our location in the spiral disk is not that typical. The density of stars in the spiral varies.

The same issues that make it difficult to estimate the number of stars also make it hard to know our galaxy's exact structure and shape. It took a lot of effort to discover that we have a bar in the middle of it and that our galaxy is a barred spiral. We also eventually figured out that we are in a mini arm called the Orion Spur, smaller than the two primary arms, the Perseus and Scutum-Centaurus. Even more recently, we determined that our galaxy's spiral disk is not flat but slightly twisted. These features would be easily visible if we could view our galaxy from a distance of millions of light-years.

Furthermore, our location within also makes it hard to know what is outside of our galaxy in the direction of the bulge and the plane of the spiral disk. Our Local Group of galaxies, including the Milky Way, Andromeda, and their satellites, are moving towards the point in the sky obscured by the central bulge. Gravitational anomaly millions of times more massive than our galaxy was identified there and named the Great Attractor. Because it's so difficult to survey this part of the sky, it was discovered recently that this is not even the whole story. There is another even bigger overdensity of matter even further in this direction called Shapley Attractor, to which the Great Attractor and we are moving.

The question was: For a long time,e the Milky Way Galaxy had 100 billion stars, but the figure was changed to 400 billion stars. Why was the number of stars revised? Is there a rationale for the change?

Our galaxy has two primary arms, the Perseus and Scutum-Centaurus, but we are in a smaller Orion Spur arm.

It has recently been discovered that the disk of our galaxy is not flat but slightly twisted.

Our galaxy is being pulled by the Great Attractor and an even more massive Shapley Attractor behind it that happen to be in the part of the sky obscured by the bright bulge and plane of our galaxy.