Which is the biggest mystery in space science?

 Blackhole.

Why?

• It can't be seen. Yes! a blackhole cannot be detected neither with a telescope nor by any spacecraft, yet it is found to exist.
• It doesnot emit radiation. Being the most massive objects of the Universe ( an object of infinite mass ), it doesn't emit it's own radiation rather it is detected by the radiation given off by the body which is in it's acreetion disk. On the contrary, every body in this universe that has mass is found to emit radiation. An 'atom' ( basic structural unit of everything around us ) also emits radiation.
• If you wish to remain forever young, you should prefer going into a Blackhole. It's​ gravitational pull is so massive that even light cannot escape it's surface, time inside the blackhole stops.

• Even you can become a black hole. Theoretically,any object compressed to very high density has the potential of becoming a Blackhole.
• Despite being so massive, they can evaporate with time.

• Don't be surprised when a 5 ft 7′ guy suddenly looks like a 6 ft 4′ ! A phenomenon called 'spagehttification' takes place as your feet tend to get more closer to the center of Blackhole.

P.S.: No one is able to ascertain firmly the reason for all these phenomenon. The concept of Blackhole though discovered over a 100 years ago, still remains a matter of debate to the leading scientists of the World.

How do stars survive in intergalactic space?

 Millions of "rogue" stars have been violently ejected into the empty voids between galaxies. They don't just survive in the dark—this absolute isolation is the safest place a star can be.

A star's existence has nothing to do with its galactic environment. It is simply a massive ball of gas held together by its own gravity, engaged in a constant tug-of-war with the outward pressure of nuclear fusion at its core. As long as a star has enough mass to maintain fusion, it is entirely self-sufficient. It does not rely on a host galaxy for fuel, warmth, or structural support.

Inside a galaxy, stars face several gravitational hazards. They can be disrupted by passing stellar neighbors, swallowed by central supermassive black holes, or caught in the blast wave of a nearby supernova. Out in the intergalactic void, a rogue star is entirely free from these threats, left to burn its fuel in total peace.

Stars are born inside the gas-rich nurseries of galaxies, but violent gravitational interactions can forcibly eject them. When two galaxies collide, the chaotic shifting of gravitational fields can fling millions of stars out into the void in long, trailing "tidal tails." Alternatively, in a process known as the Hills mechanism, a binary star system wandering too close to a galaxy's central supermassive black hole can be torn apart. One star is captured by the black hole, while the other is violently slung outward at millions of miles per hour—fast enough to break free of the galaxy's gravitational grip entirely.

Once ejected, an intergalactic star faces a long, solitary timeline. Because there are no heavy molecular clouds in intergalactic space, a rogue star's death will not trigger the birth of new stars. It will simply consume its internal hydrogen reserves over billions of years, eventually swelling into a red giant and quietly collapsing into a white dwarf, neutron star, or black hole in the dark.

The reconstructed orbits of 20 high-velocity stars that are escaping the Milky Way's gravitational pull into intergalactic space. Photo by ESA is licensed under CC BY-SA 3.0 igo.

Why is space holding planets?

 Space isn't actually holding the planets up at all. Earth is locked in a perpetual freefall, hurtling sideways at 67,000 mph just fast enough to constantly miss the Sun.

To understand why planets stay in place, you first have to discard the idea of "up" and "down." On Earth, if you drop a rock, it falls down. But in the wider universe, "down" does not exist as a universal direction. Down is simply the path toward the center of the nearest massive object. There is no cosmic floor for planets to fall onto.

Instead of falling down, planets are constantly falling around. In 1915, Albert Einstein revolutionized our understanding of gravity by proposing that space and time are woven together into a four-dimensional fabric called spacetime.

Imagine stretching a large trampoline tight and placing a heavy bowling ball in the center. The ball causes the fabric to sink, creating a deep funnel. This is what the Sun does to spacetime. If you take a marble—representing a planet like Earth—and roll it sideways along the rim of that funnel, it won't drop straight to the center. It will circle the bowling ball.

Earth's natural tendency is to travel in a straight line out into deep space, but the steep curve of the Sun's gravity well constantly bends that straight path into a circle. The precise balance of forward momentum and the inward pull of curved space results in a stable orbit.

Are there any objects in space that are smaller than stars but larger than planets, such as brown dwarfs?

 If you packed 70 times more mass into Jupiter, it wouldn't get any wider. It would become a brown dwarf—a "failed star" trapped in the cosmic middle ground between planets and true stars.

To understand what a brown dwarf is, it helps to look at the firm mass boundaries that define stars and planets:

• A star is an object massive enough that the crushing pressure and heat in its core ignite the sustained nuclear fusion of regular hydrogen (hydrogen-1). The absolute minimum mass required to do this is roughly 80 times the mass of Jupiter.
• A planet like Jupiter does not have enough mass to ignite any kind of nuclear fusion. It generates no internal fusion energy and simply cools down over time.

If an object forms with a mass between roughly 13 and 80 times that of Jupiter, it falls directly into this middle ground. Unlike true planets, brown dwarfs are massive enough that their core pressure ignites nuclear fusion—but only the fusion of deuterium, a heavy isotope of hydrogen. Because deuterium is scarce, a brown dwarf burns through its supply in a few million years, which is a blink of an eye in cosmic terms.

Once the fuel is gone, the fusion stops. For the rest of its long life, the brown dwarf glows faintly in the infrared spectrum from leftover heat, slowly fading and cooling until it turns pitch black.

This size paradox is one of the most unintuitive physical properties of brown dwarfs. Due to the quantum mechanics of electron degeneracy pressure, adding mass to a brown dwarf does not make it physically larger—it just makes it denser. Gravity pulls the extra mass inward so tightly that a heavy brown dwarf remains almost exactly the same diameter as Jupiter.

A size comparison showing a low-mass star, a brown dwarf, and Jupiter. Due to extreme density, a brown dwarf has roughly the same physical volume as Jupiter despite being up to 80 times more massive. Source: Wikimedia Commons.

For decades, these objects only existed in mathematical theories because they emit almost no visible light. Astronomers finally found undeniable proof in 1995 with the discovery of Gliese 229B. Spotted orbiting a red dwarf star, it glowed faintly in the infrared, and its atmosphere contained methane—a molecule that cannot survive the intense heat of a true star. At the very bottom of the brown dwarf temperature scale, astronomers have now even found Y-dwarfs, which have cooled down so much that their atmospheres match the temperatures of a warm summer day on Earth.

What are the implications of space and time having no beginning or end?

 If space and time have no beginning or end, they create a mind-bending paradox: the universe should already be dead, and an exact replica of your life will repeat endlessly.

The most immediate problem an eternal universe creates is thermodynamic. The Second Law of Thermodynamics dictates that entropy—disorder—always increases. In a closed system with a finite amount of usable energy, an infinite amount of time guarantees that the system reaches "heat death." All stars would burn out, all black holes would evaporate, and space would settle into a uniform, freezing radiation bath. If the universe is infinitely old, it should already be in this dead state.

To avoid this paradox, an eternal universe requires a physical mechanism for renewal. This points toward cyclic models, where the universe undergoes endless sequences of expansion and contraction, resetting the entropy clock with each "Big Bounce." Alternatively, theories like eternal inflation propose that our visible universe is just one finite bubble in a constantly expanding multiverse where new regions of space continuously spark into existence.

An infinitely old and large universe also invokes the Poincaré recurrence theorem. In a bounded region of space, there is a finite number of ways matter and energy can be arranged. If time stretches infinitely into the past and future, every possible configuration of quantum states must eventually occur, and reoccur an infinite number of times. Every variation of history plays out endlessly across the expanse.

This infinite timeline eliminates the necessity of a "First Cause." Cosmological arguments for a creator rely on the premise that a finite chain of events must have a starting point. An eternal universe exists as a brute fact, requiring no genesis because there was never a "before" to trigger it.

Webb’s First Deep Field shows thousands of galaxies, including some of the faintest objects ever observed in the infrared, hinting at the vast scale of the cosmos. Source: Wikimedia Commons.

What are some of the most amazing facts about space?

 

• 1. Neutron stars can spin at a rate of 600 rotations per second.

• ​
  
  Neutron stars are one of the possible evolutionary end-points of high mass stars. They're born in a core-collapse supernova star explosion and subsequently rotate extremely rapidly as a consequence of their physics. Neutron stars can rotate up to 60 times per second after born. Under special circumstances, this rate can increase to more than 600 times per second.
  Source: Swinburne University of Technology Centre for Astrophysics and Supercomputing
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 2. All of space is completely silent.

• ​
  
  Sound waves need a medium to travel through. Since there is no atmosphere in space, space will always be eerily silent.
  You may be asking how astronauts can talk to each other in space. Lucky for them, radio waves cantravel through space. No problem there, Houston.
  Source: Cornell University Department of Astronomy
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 3. There is an uncountable number of stars in the known universe.

• ​
  
  We basically have no idea how many stars there are in the universe. Right now we use our estimate of how many stars there are in our own galaxy, the Milky Way. We then multiply that number by the best guesstimate of the number of galaxies in the universe. After all that math, NASA can only confidently say that say there all zillions of uncountable stars. A zillion is any uncountable amount.
  An Australian National University study put their estimate at 70 sextillion. Put another way, that's 70,000 million million million. This figure is basically a guess, though.
  Sources: University of California at Santa Barbara ScienceLine,
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 4. The Apollo astronauts' footprints on the moon will probably stay there for at least 100 million years.

• ​
  
  Since the moon doesn't have an atmosphere, there's no wind or water to erode or wash away the Apollo astronauts' mark on the moon. That means their footprints, roverprints, spaceship prints, and discarded materials will stay preserved on the moon for a very long time.
  They won't stay on there forever, though. The moon still a dynamic environment. It's actually being constantly bombarded with "micrometeorites," which means that erosion is still happening on the moon, just very slowly.
  Source: Space.com
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 5. 99% of our solar system's mass is the sun.

• ​
  
  Our star, the Sun, is so dense that it accounts for a whopping 99% of our entire solar system. That's what it allows it to dominate it gravitationally. Technically, our Sun is a "G-type main-sequence star" which means that every second, it fuses approximately 600 million tons of hydrogen to helium. This means that it also converts about 4 million tons of matter to energy as a byproduct.
  Being the type of star that the Sun is, it also means that when it dies, it will become a red giant and envelop the earth and everything on it. But don't worry: That won't happen for another 5 billion years.
  Source: The Ohio State University Department of Astronomy
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 6. More energy from the sun hits Earth every hour than the planet uses in a year.

• ​
  
  You should be sad to know that solar technology produces less than one-tenth of 1% of global energy demand. This is due to several factors, including how much land is required for solar panels to capture enough energy for a population of people to use, how unreliable it is in bad weather and at night, and how expensive the technology is to install.
  Despite all these drawbacks, the use of solar energy has increased at a rate of 20% each year for the past 15 years.
  Source: National Geographic
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 7. If two pieces of the same type of metal touch in space, they will bond and be permanently stuck together.

• ​
  
  This amazing effect is called cold welding. It happens because the atoms of the individual pieces of metal have no way of knowing that they are different pieces of metal, so the lumps join together. This wouldn't happen on earth because there is air and water separating the pieces. The effect has a lot of implication for spacecraft construction and the future of metal-based construction in vacuums.
  Source: European Space Agency
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 8. The largest asteroid ever recorded is a mammoth piece of space rock named Ceres.

• ​
  
  The asteroid is almost 600 miles in diameter. It's by far the largest in the asteroid belt and accounts for a whole third of the belt's mass. The surface area is approximately equal to the land area of India or Argentina. It's so big, there's actually some debate over whether to refer to it as a dwarf planet instead of an asteroid, even if it has mostly asteroid-like qualities.
  Ceres piques our interest specifically, as water in the form of ice has been spotted on its surface. An unmanned spacecraft named Dawn is due to be orbiting the space rock by 2015.
  Source: TheGuardian.com
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER

Could there be a planet with 99% oxygen in space?

 We actually already know of one, but it's a moon, not a planet!

And yet it is so thanks to a small loophole.

This is Europa. It's a moon of Jupiter and is slightly smaller than our Moon. Its surface is composed of layers of ice, probably with liquid water deeper down. On the ice, this moon is constantly bombarded by deadly radiation (caused by the nearby volcanic moon Io and Jupiter's immense magnetic field).

Its atmosphere is composed almost exclusively of oxygen. But oxygen is so rare in the universe, so where does it come from? While oxygen on Earth is formed by plants, the oxygen on Europa is formed by radiation passing through the ice, splitting water molecules into hydrogen and oxygen gas (the hydrogen escapes into space).

But you couldn't breathe in it! Why?

Because Europa's atmosphere is actually very, very, very thin. The air pressure at its surface is only a billionth of that on Earth. So it can barely be said to have an atmosphere.

So here's the loophole: You asked about a planet whose atmosphere is 99% oxygen, which is a ratio. But you didn't ask how much atmosphere there is in the first place.

What is Light’s relationship to Time and Space?

 A photon traveling 2.5 million years from the Andromeda galaxy to Earth experiences exactly zero seconds of time. To light, time and space simply do not exist.

In the early 20th century, Albert Einstein realized that the speed of light in a vacuum is the single fixed constant of the universe. Before this, physicists believed space and time were a rigid background stage on which events simply happened. Einstein showed that space and time are actually flexible, bending and stretching to ensure that the speed of light always remains exactly the same for any observer. This relationship binds the two dimensions together into a unified fabric known as spacetime.

Because the speed of light dictates the rules of this fabric, objects moving through spacetime experience fascinating mechanical effects as they accelerate:

• Time Dilation: As an object moves faster through physical space, its movement through time slows down relative to outside observers. If a person were to travel in a spaceship at 99 percent of the speed of light, people observing from Earth would see the traveler's clock ticking in slow motion. For a photon, which travels exactly at the cosmic speed limit, the clock stops entirely. A photon does not experience time; it never ages.
• Length Contraction: Speed also compresses physical distance. To a fast-moving object, the space ahead physically shrinks. For a photon, that distance contracts all the way to zero. When a particle of light travels across the entire observable universe, its point of departure and its point of arrival are, from its own frame of reference, exactly the same place.

Light does not merely travel through space and time; it defines their very boundaries. The speed of light acts as the ultimate conversion rate between the two, which is why astronomers measure cosmic distances in light-years. It is the fundamental stitch holding reality together, acting as the universe's absolute speed limit to ensure that cause always precedes effect.

What is the most shocking photo you have ever seen?

 I wanted to share some truly amazing space photos. I'm sure you'll all be amazed when you see them:

1. The amazing phenomenon of a lightning tornado occurring above an erupting volcano.

2. Photographer Leonardo Sens waited for 3 years to take this fantastic photo in Rio De Janeiro, Brazil.

3. The small black dot in front of the sun is the planet Mercury.

4. A "leaked" photo from NASA has been circulating showing them repairing ( maintenance ) the sun. 😁

5. One of the most detailed photos of the planet Saturn.

6. Likewise with Pluto, this is one of its most detailed photos.

7. The sharpest photo of the planet Venus.

8. The most detailed photo of the sun.

9. A year's worth of amazing sunrise photos.

10. The Amazon River seen from space.

What are some really interesting, lesser known facts about space?

 Space travel changes the shape of Astronaut’s heart

From feelings of weightlessness to literally out-of-this-world views, the life of an astronaut is something to be envied—most of the time. Unfortunately, space is also really bad for the human body. According to a NASA study, it's bad for the human heart, too: time in space makes astronauts' hearts more spherical.

Gym buffs know you lose muscle mass when you don't work out regularly. Same goes for a heart in microgravity. "The heart doesn't work as hard in space, which can cause a loss of muscle mass," said James Thomas, M.D., ultrasound lead at NASA, in an American College of Cardiology news release.

For the study, 12 astronauts learned how to do ultrasounds so they could image their hearts before, during and after space travel. The NASA researchers found that their hearts became 9.4 percent more spherical, which could be a sign the muscle is not working as efficiently. Luckily, their hearts returned to their normal shapes once they were back on Earth, but the effects a longer spaceflight could have are anyone's guess.

There's a silver lining in all of this. The study not only tested what microgravity does to hearts in space—it also tested sophisticated mathematical models that the researchers had developed to predict what the hearts might do. The final results matched what their models had predicted, which means that they might be able to use them to predict what other, more earthly elements might do to the heart.

"It gives us confidence that we can move ahead and start using these models for more clinically important applications on Earth, such as to predict what happens to the heart under different stresses," said Thomas, also of Northwestern Medicine, in the 2014 release. That means the astronauts' heart images could eventually help scientists learn more about cardiac conditions that affect people on this planet

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Atronauts can actually see COSMIC RAYS in the space

The first person to report seeing cosmic rays was none other than Buzz Aldrin. During the Apollo 11 mission in 1969, he mentioned seeing strange flashes of light that took on a variety of shapes and dimensions. When astronauts say they're seeing things, people take them seriously, so by the time Apollo 16 and 17 took off there was a special detector on board to figure out what was going on. The results? The flashes were caused by high-energy charged particles, the stuff of cosmic rays. Over many more missions, the research continued, showing that the particles affected every astronaut differently: some could see them in bright conditions while others could only see them in the dark; some were so bothered by them that they had trouble sleeping while others couldn't see them at all.

Here's the problem: cosmic rays aren't just sci-fi jargon. They're really harmful. Specifically, they're radioactive fragments of atoms—mostly protons, but also some neutrons and electrons—that move at incredibly high speeds and tear through any molecules unlucky enough to be in their path. They're the reason radiation is a primary concern on future missions to Mars. The fact that astronauts are seeing them means that cosmic rays are hurtling into astronauts' eyes. Not good.

We know the flashes are cosmic rays, but we don't actually know the reason astronauts are seeing them. The rays aren't light, after all—they're just radioactive particles. Researchers have formed three theories about why astronauts can see them: one was that they were entering the eye and hitting the optic nerve. Another was that they were entering the astronauts' skulls and hitting the vision center of the brain.

The third theory is definitely scariest: the particles are traveling through the vitreous humor of the astronauts' eyes and emitting light in the form of something called Cherenkov radiation. As io9 puts it, "The light is coming from inside their eyeballs."

How far will the Voyager 1 actually travel before it stops?

 As of March 2026, Voyager 1 is approximately 23.5 to 24 light-hours away from Earth. The probe is over 24 billion kilometers (15 billion miles) away and is expected to reach the milestone of being one full light-day—24 hours—away from Earth by November 2026. Currently it is in interstellar space, having passed the heliopause.

Voyager 1 uses nuclear batteries that have been qorking since 1977, but will probably exhaust by 2036. Then this probe will be totally useless, disconnected and dead metal.

It will go on traveling. It is very unlikely that it will hit something. It will take tens of thousands of years before it reaches another star system. Now it takes 47 hours to send a command to it and get the feedback or response. If it will fall into the hands of an intelligent alien race after one hundred thousand years, by that time it might be possible human will no longer exist. So sad.

Could black holes be shortcuts through space and time?

 Yes,it is theoretically possible but not in a practical way. According to GR, space and time are not two mutually independent dimensions but connected through space-time fabric.When an object of masses are there,it create space time curvature on that fabric. Since black hole have very high density ,so it creates an enormous amount of curvature.

Now, think space time fabric as a thin piece of paper,where by folding it in a way that two distant points are closed by a tiny tunnel (as here the width of the paper). This is possible also in a real case of space time geometry.And that tiny tunnel are shortcuts through space-time between two locations of the universe.

That tunnel(also known as worm hole) connects two different locations where one side is a black hole and opposite site there is a white hole.

Though this idea is highly speculative and it is believed that wormholes are highly unstable. It would be saying too much speculation that we could do time travel by that wormhole.

The deepest problem is that we have zero observational evidence that wormholes exist at all. They are valid solutions to Einstein's field equations, but mathematical possibility doesn't guarantee physical reality.

With the super clear cameras today, why are the photos from space vehicles so bad?

 I honestly can’t figure out what you are talking about.

Here is a picture of Europa taken by Voyager 2 almost 40 years ago. Quora can’t even show it in full detail.

In comparison, this is a Galileo picture of Europa from 25 years ago.

More recently New Horizons took this picture of Charon, the sister world of Pluto.

Keep in mind that the Sun’s light is so dim at Charon, it’s like taking a picture of the Earth with barely more than moonlight. (That is a little hyperbole. It’s more like a floodlit building at night. See the comment below.)

Maybe you are confused because pictures of gas giants do not look as detailed?

That’s a case of the picture is sharp, but Jupiter isn’t so sharp and contrasty, because, well, it is a nebulous gas that you are looking at.

Maybe it is Hubble pictures that you feel are not sharp.

Well, again, you are looking at a nebula.

Could you give an example of pictures from space vehicles that you do not think are clear?

Maybe you don’t like the Hubble Deep Field photos?

Keep in mind you are looking at a tiny patch of sky that has been magnified considerably. Also remember that before Edwin Hubble discovered that Andromeda was actually a galaxy, they were called “nebulae” because they appeared fuzzy.

Or maybe you thought this picture of the Earth taken from the International Space Station is not clear enough.