00:00Did you know that the stars in the sky are distant suns?
00:04They are all huge spheres of hydrogen gas.
00:07Fusion takes place in the core of stars.
00:09Four hydrogen atoms fuse into one helium atom, and in the process, light is generated.
00:14Light doesn't reach the surface instantly.
00:16In the sun, the journey takes tens of thousands of years.
00:19Depending on their surface temperature and spectral characteristics,
00:23astronomers have determined that there are seven types of ordinary stars,
00:27from the hottest to the coolest, O, B, A, F, G, K, and M.
00:31Temperature is an important characteristic of stars.
00:34It is what gives them their color.
00:36It's basically the opposite of the faucet's hot and cold indicator.
00:39When the color is redder, the stars are cooler, and when the color is blue, the stars are hotter.
00:45These can also be up to five times hotter than our sun.
00:48The bigger the star, the more outer layers it has, and the more pressure is exerted on its core.
00:54So, the hydrogen there fuses more intensely.
00:57That's why bigger stars are brighter and hotter.
01:01Paradoxically, they live shorter lives because it's like straw.
01:04They burn faster.
01:05After what you've heard here, can you say whether the stars from the beginning of the universe,
01:09which formed when the hydrogen density was high, lived short or long lives?
01:15Did you know that there are failed stars in the universe,
01:18meaning stellar objects that never ignite because they're too small?
01:21So, their weak gravity doesn't manage to trigger hydrogen fusion.
01:25They're called brown dwarfs, and they're bigger than Jupiter.
01:29Brown dwarfs don't have enough mass to sustain the continuous fusion of hydrogen in their cores,
01:34a process that powers conventional stars.
01:37With masses between 13 and 80 times greater than Jupiter's, but less than about 8% of the sun's mass,
01:44brown dwarfs don't generate significant heat or light, which leads to their gradual cooling and dimming.
01:50Over time, they emit mainly light in the infrared spectrum,
01:53making them hard to detect with optical telescopes in the visible spectrum.
01:57With infrared telescopes, however, their spectra are dominated by molecules like methane, ammonia, and water,
02:03which makes them easier to identify.
02:05Brown dwarfs tend to have rapid rotation periods,
02:09with some spinning on their axis in just a few hours.
02:12Since their discovery in the 1990s, brown dwarfs have become an active field of research in astrophysics.
02:18They help us understand exoplanets as well,
02:21since they share many features with gas giant planets, such as their atmosphere.
02:28Did you know that red dwarf stars can live for trillions of years?
02:32Red dwarfs are born a little larger than brown dwarfs.
02:35The red color reveals their low temperature.
02:38The gravity of red dwarfs is barely strong enough to ignite hydrogen fusion.
02:43They shine faintly and cannot be seen with the naked eye in the sky.
02:47Red dwarfs are the most common type of star in the galaxy,
02:51making up about 75% of all stars.
02:53They are relatively small and have a temperature between 2500 and 3000 degrees Celsius,
02:59with a mass that ranges from about 0.075 to 0.5 times the mass of the sun,
03:05which places them significantly below the mass of our sun.
03:09That's why they emit only a fraction of the energy that stars like the sun produce.
03:14What makes them special is their longevity.
03:17Red dwarfs burn their nuclear fuel much more slowly than larger stars,
03:21with lifespans that can reach trillions of years.
03:25This extended lifespan exceeds the current age of the universe,
03:29which means that no red dwarf has yet died a natural death.
03:33Many red dwarfs have exoplanets orbiting them.
03:36Because they don't emit much ultraviolet light,
03:39the conditions on planets orbiting close to them could be suitable for supporting life.
03:44Because it doesn't emit much ultraviolet light,
03:46where seven planets orbit a dwarf star.
03:49Red.
03:50That's why a telescope like James Webb is searching for habitable exoplanets orbiting around red dwarfs
03:56close to them, where it's warmer.
03:58Despite the challenges, such as stellar flares caused by strong magnetic fields,
04:02there is hope that on an exoplanet around a red dwarf,
04:06we might discover life for the first time.
04:11Did you know the sun is a yellow dwarf?
04:14Stars called yellow dwarfs are larger than those called red dwarfs.
04:18That's why fusion becomes more efficient,
04:20shortening their lifespan to just a few tens of billions of years.
04:24Yellow dwarf stars, like our sun,
04:26are a class of medium-sized stars on the main sequence,
04:30characterized by their yellowish color and relatively moderate surface temperatures.
04:34They have surface temperatures ranging from about 5,000 to 6,000 degrees Celsius.
04:39Yellow dwarfs are powered by the nuclear fusion of hydrogen into helium in their cores,
04:45a process that emits a significant amount of light and heat.
04:49Although they are considered dwarfs,
04:52these stars can be quite powerful and bright.
04:55Our sun, for example,
04:57has a mass about 300,000 times greater than that of Earth
05:00and radiates energy at a rate of billions upon billions of gigawatts.
05:05The lifespan of yellow dwarf stars is relatively moderate in cosmic terms,
05:09ranging between 8 and 10 billion years.
05:12As they age, yellow dwarfs become hotter and expand,
05:15eventually becoming red giants.
05:17This transformation marks the end of the stable phase of their life cycle.
05:22After losing their outer layers,
05:24a white dwarf may remain behind.
05:26Yellow dwarfs are important to us.
05:28Their stability and longevity make them favorable for planets.
05:33That's why space telescopes search for Earth-like planets around yellow dwarfs.
05:39What do you think?
05:40Will they manage to find one?
05:42We live in the internet age,
05:43but people elsewhere on this planet experience the internet differently.
05:47When I want to explore other countries virtually,
05:49I use a VPN to see what the world looks like from those countries.
05:52Surfshark is a VPN that gives you access to the entire Netflix movie database
05:56and cheaper subscriptions to some platforms like YouTube, Premium, HBO, and so on.
06:01Surfshark hides your IP address and thus ensures your virtual privacy while browsing the internet.
06:06You can search for plane tickets and hotel rooms at lower prices,
06:10and the app has a minimalist, user-friendly design.
06:13With the Surfshark Alert Service from Surfshark One,
06:16you can monitor your data, check for possible breaches,
06:18receive alerts, and benefit from real-time protection.
06:21And Surfshark Antivirus helps you keep your device virus-free,
06:25perform a quick or full scan of your device,
06:27benefit from real-time protection, and run quick scans.
06:30Or secure your privacy with Surfshark.
06:33Go to my link in the description and enter the promo code PREJURA,
06:36and you'll get four months free.
06:40Did you see the blue star in the sky?
06:43It's called Spica, and in reality, it's a spectroscopic binary star,
06:47which means it's made up of two stars that orbit so close to each other
06:51that they can't be visually separated.
06:54One of them is a blue giant, a star ten times bigger than the sun.
06:58Its blue color proves that it's much hotter than the sun.
07:02Hydrogen fusion is so efficient that Spica burns out in just a few tens of millions of years.
07:07Because of its brightness, we can see it with the naked eye,
07:10even though it is very far away.
07:12Red giants and blue giants represent different stages and classifications of stars in the universe.
07:18Red giants are stars at the end of their lives
07:21when they have exhausted the hydrogen in their core
07:24and begin to fuse helium into heavier elements.
07:27This final stage lasts for several billion years.
07:30As the star's core contracts and heats up,
07:33the outer layers of the star expand dramatically,
07:35cooling and turning red in the process,
07:38which is why they are called red giants.
07:41These stars can swell up to sizes that are hundreds of times larger than their original size.
07:47In contrast, blue giants are massive stars right from the beginning of their lives.
07:52They fuse fuel much faster than smaller stars, like our sun.
07:57Blue giants are hot and luminous,
07:59with surface temperatures ranging from 10,000 to 50,000 degrees Celsius,
08:04giving them a distinctive blue hue.
08:07Because of their large masses,
08:09the fusion process is more efficient,
08:11which shortens their lifespan,
08:13often ending in dramatic supernova explosions.
08:16Both types of giants have played a role in making us what we are today.
08:19While red giants contributed to the synthesis of heavy elements
08:22and their distribution in space,
08:24blue giants often ended their lives,
08:27in the form of supernova explosions,
08:29seeding the universe with even heavier elements,
08:32thus contributing to the chemical diversity of the universe.
08:36The heavy atoms in you were once part of such giant stars.
08:43Did you know that UY Scuti,
08:45sometimes classified as a red hypergiant,
08:47is the largest star known to us
08:49and has a radius 1,700 times larger than the sun's?
08:54Hypergiant stars are among the most massive and luminous stars in the universe,
08:58representing the extreme upper limit of stellar evolution.
09:02Because they are so large,
09:03the fusion process is very efficient
09:05and that means a lot of energy.
09:07Due to their colossal energy output,
09:10hypergiants are often unstable.
09:12They lose matter through strong stellar winds,
09:15matter that can then contribute to the formation of nebulae.
09:20Hypergiants are classified into two main types,
09:22based on their temperature.
09:24Blue hypergiants, which are extremely hot and often more luminous,
09:28and red hypergiants, which are cooler but still incredibly bright.
09:32Examples include eta carini, a well-known blue hypergiant,
09:36and VY Canis Majoris, one of the largest known red hypergiants.
09:41Hypergiant stars play a significant role
09:43in enriching their galaxies with heavy elements,
09:46which are essential for the formation of new stars and planets,
09:49and for the possibility of life appearing in the universe.
09:52They end in spectacular and violent explosions,
09:55such as supernova explosions,
09:57leaving behind a neutron star or even a black hole.
10:00Thank you for watching the video until the end,
10:03and thanks to Surfshark for sponsoring.
10:05Don't forget about my link in the description.
10:08That way you ensure your privacy with Surfshark
10:10and get four months free.
10:11Until next time, I'm Christian Persura.
10:13You are all super cool, and I wish you all the best.
10:16Goodbye.
10:16Goodbye.
Comments