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One of the many mysteries baffling astronomers is how galaxies such as the Milky Way are able to form new stars at an unsustainable rate. (NASA / JPL)

Top Ten Mysteries of the Universe

What are those burning questions about the cosmos that still baffle astronomers today?

6. Galactic Recycling

In recent years, astronomers have noticed that galaxies form new stars at a rate that would seem to consume more matter than they actually have inside them. The Milky Way, for example, appears to turn about one sun’s worth of dust and gas into new stars every year, but it doesn’t have enough spare matter to keep this up long-term. A new study of distant galaxies might provide the answer: Astronomers noticed gas that had been expelled by the galaxies flowing back in to the center. If the galaxies recycle this gas to produce new stars, it might be a piece of the puzzle in solving the question of the missing raw matter.

7. Where Is All the Lithium?

Models of the Big Bang indicate that the element lithium should be abundant throughout the universe. The mystery, in this case, is pretty straightforward: it doesn’t. Observations of ancient stars, formed from material most similar to that produced by the Big Bang, reveal amounts of lithium two to three times lower than predicted by the theoretical models. New research indicates that some of this lithium may be mixed into the center of stars, out of view of our telescopes, while theorists suggest that axions, hypothetical subatomic particles, may have absorbed protons and reduced the amount of lithium created in the period just after the Big Bang.

8. Is There Anybody Out There?

In 1961, astrophysicist Frank Drake devised a highly controversial equation: By multiplying together a series of terms relating to the probability of extraterrestrial life (the rate of star formation in the universe, the fraction of stars with planets, the fraction of planets with conditions suitable for life, etc.) he surmised that the existence of intelligent life on other planets is extremely likely. One problem: Roswell conspiracy theorists notwithstanding, we haven’t heard from any aliens to date. Recent discoveries of distant planets that could theoretically harbor life, though, have raised hopes that we might detect extraterrestrials if we just keep looking.

9. How Will the Universe End? [Warning, Potential Spoiler Alert!]

We now believe the universe started with the Big Bang. But how will it end? Based on a number of factors, theorists conclude that the fate of the universe could take one of several wildly different forms. If the amount of dark energy is not enough to resist the compressing force of gravity, the entire universe could collapse into a singular point—a mirror image of the Big Bang, known as the Big Crunch. Recent findings, though, indicate a Big Crunch is less likely than a Big Chill, in which dark energy forces the universe into a slow, gradual expansion and all that remains are burned-out stars and dead planets, hovering at temperatures barely above absolute zero. If enough dark energy is present to overwhelm all other forces, a Big Rip scenario could occur, in which all galaxies, stars and even atoms are torn apart.

10. Across the Multiverse

Theoretical physicists speculate that our universe may not be the only one of its kind. The idea is that our universe exists within a bubble, and multiple alternative universes are contained within their own distinct bubbles. In these other universes, the physical constants—and even the laws of physics—may differ drastically. Despite the theory's resemblance to science fiction, astronomers are now looking for physical evidence: Disc-shaped patterns in the cosmic background radiation left over from the Big Bang, which could indicate collisions with other universes.


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