“Old smokers”, “squealing newborns“ — and the star lifecycle in between!
Space Nuggets #9: When astronomers embarked on a study to observe a category of stars, they also made an accidental discovery of a whole new type of star! Read on to find out how these stars were discovered and everything in the lifecycle of a star in between.
Hi everyone, welcome to the overall 9th edition of the fortnightly series of Space Nuggets! Space Nuggets are bite-sized pieces on the latest astronomy events and the phenomenon behind them, intending to share the marvels of the world around us and the Universe with one and all!
In this article, meet the “old smokers” and the “squealing newborns” — the recently-famous “star kids” on the block — and find out how they come into existence in the Universe!
Stars are one of the brightest objects we can see in our night sky, after the Moon and some planets (from time to time), and we can see thousands of them any evening from galaxies far and wide. They have been known by civilizations for eons and as a part of early astronomy, they served us well as our calendars for farming, traveling to interesting stories about constellations that have survived the test of time and are with us even today.
But, stars have very fascinating lives of their own too. They are so powerful that they build a whole planetary system around themselves — where who knows life exists just like our planet — and they can also lead to super dramatic events like supernovae and gamma ray bursts from a blackhole — which in turn becomes the birthplace for new stars! Thus, as one of the better-documented objects of the night sky, we thought we had them all figured out — until we found something more.
In the research([1],[2],[3],[4]) published on 26th Jan by the Royal Astronomical Society, scientists were able to observe 2 new kinds of stars by studying the center of our Milky Way Galaxy for over 10 years. The funny thing is that they started with the mission to observe closely just 1 category (the squealing newborns or the protostars) — but they got rewarded with a view of this and a whole new category (called the old smokers).
But before we jump into what these stars are, how they were discovered, and how they came to be, let’s quickly brush up on the stars we know today!
Lifecycle of a star
The birth of any star takes place in a nursery of gas and dust called a “nebula” when enough mass of gas and dust clump together so that it collapses under its gravity and starts burning its fuel — mainly the hydrogen gas. This very nascent stage of a star is called a “protostar” — yes the one for which the study was commissioned!
Based on the size and mass of the newborn, there are different categories of stars, and this also determines their future life. Stars like our Sun shine yellow, and they are not that huge. But stars with mass 8–10 times our Sun are the “blue stars” — one of the biggest and brightest stars in our Universe. Rigel in the Orion constellation is one of them, which is why it is so bright in the night sky even though it is 870 light years away!
Blue stars are huge, but they are also super hot (hence the color blue!) and burn through their fuel super quickly and thus have a very short lifespan. On the other hand, our Sun is a yellow dwarf and has a longer lifespan.
At this stage, stars are using hydrogen as fuel and creating helium through nuclear fusion. This generates heat and the outward radiation pressure which balances gravity.
Once both of these types of stars run out of hydrogen as fuel, they transform into “Red stars”, supergiants and giants respectively — where they are burning heavier elements for fuel, hence having lesser energy compared to nuclear fusion of hydrogen. This is when their core becomes smaller and unstable, and they do not generate as much heat and start cooling off. Hence the red color! But there are still remnants of hydrogen in the plasma around, and nuclear fusion here leads to enough outward radiation pressure for this thin layer to expand — hence a giant.
Once the core starts making iron, it requires more energy for fusion than it releases and collapses under its gravity, finally exploding to form a planetary nebula (if it was a yellow dwarf) or a supernova (if it was a blue giant) — in the process creating all those precious metals like gold, silver, and platinum. Both of these emit a huge amount of gas and dust, where new stars will be born. The same surrounding dust also forms planets, asteroids, and everything else in the Universe, including us.
The old stars’ core itself will become small and cold and form a white dwarf in the case of the dwarf stars. Though a supernova creates such a strong force during the explosion that if the remnant is 1.4–3 times the mass of the Sun, it will collapse into a very dense core of neutrons called a neutron star. If the remnant is >3 times the mass of the Sun, gravity wins over the force of explosion and everything collapses into a black hole — where gravity is so strong that even light cannot pass through it.
How were protostars observed for the first time?
Since protostars are the very early stages of any star, they are still in the nebula, where they are surrounded by thick gas and dust. These absorb light in the visible range and hide the protostars from our view. But with the Visible and Infrared Survey Telescope (VISTA) telescope using infrared rays, we have been able to observe them at the heart of the Milky Way galaxy for the first time.
Stars here which showed great outbursts, and hence sudden changes in brightness, were studied more closely as these are likely candidates for protostars. This is because these outbursts happen in the slowly spinning disc of matter around the star (trying to form a planetary system). Such outbursts (so strong that the stars shine at a magnitude 40 times to 300 times their original brightness) help the star to grow, but it makes it difficult for the planets to form. Once this stage is completed, the star is past its nascent stage of evolution and picks up one of the paths mentioned above depending on its mass.
Astronomers confirmed such 32 erupting protostars by looking at their spectra, hence confirming they were in their early stages, ie made of hydrogen and devoid of heavy metals.
But wait! Here’s an interesting twist — a surprise discovery
While studying these stars, the researchers found a whole new category of stars that were so dim initially that they were almost invisible — but from time to time, they would erupt, spewing off gas like puffs of smoke and hence named “old smokers”.
Initially, the scientists were unsure if these were just “protostars”, but while studying the spectra, they found out that these are, similar to red giant stars, and thus in the late stages of their lives. Scientists found 21 such old smoker red giants in the center of the Milky Way
What do old smokers and squealing stars tell us about the Universe?
It’s funny how 2 contrasting objects were discovered together and in the same place. Yet that’s the nature of life (and maybe the whole cosmos?) — Where one thing dies, another thing is born.
Studying these stars helps us understand how planetary systems evolve, how life can show up on one of them eventually, how rare precious heavy metals form, and overall understand the cosmic recycling system — similar to the water cycle we would read about in school.
Space, with its stars, galaxies, and all the other interesting objects, is like our own physics laboratory, but at a much more magnanimous scale. And stars hold a special place in our hearts — firstly because we have got only one in our Solar system to call our own — but also because they are part of all the mythological stories of different cultures we have grown up with. Yet they are not just fictional stories — observing them tells us what happened in the past hundreds and thousands of light years ago, so in a way, they are our time machines!
That’s all for this edition of Space Nuggets! Stay tuned for the next one a fortnight later, and till then, remember that we all have a little of cosmic dust inside us, so you are nothing short of stellar yourself! Happy skywatching 🔭
Do you have any suggestions for questions, phenomena, and topics you would like to see in the Space Nuggets? Reach out to me with all of these and any other feedback you have on this series 😁
References —
[1] https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stad3929
[2]https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stad3700
[3]https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stad3780
[4]https://academic.oup.com/mnrasl/article-lookup/doi/10.1093/mnrasl/slad201
