The vastness of space and the puzzling nature of the cosmic objects that occupy it provides no shortage of material for astronomers to ponder.

To round up some of the most enduring mysteries in the field of astronomy, the journal Science enlisted help from science writers and members of the Board of Reviewing Editors to choose eight puzzling questions being asked by leading astronomers today.

As Robert Coontz, deputy news editor at Science, writes in his introduction to the series, the participants decided that, "true mysteries must have staying power," rather than being questions that might be resolved by research in the near future. In fact, while some of the topics discussed may one day be solved through astronomical observations, others may never be solved, he added.

In no particular order, here are eight of the most compelling mysteries of astronomy, as presented by the journal Science:

What is dark energy? In the 1920s, astronomer Edwin Hubble discovered that the universe is not static, but rather is expanding. In 1998, the Hubble Space Telescope, named for the astronomer, studied distant supernovas and found that the universe was expanding more slowly a long time ago compared with the pace of its expansion today.

This groundbreaking discovery puzzled scientists, who long thought that the gravity of matter would gradually slow the universe's expansion, or even cause it to contract. Explanations of the universe's accelerated expansion led to the bizarre and hotly debated concept of dark energy, which is thought to be the enigmatic force that is pulling the cosmos apart at ever-increasing speeds.

While dark energy is thought to make up approximately 73 percent of the universe, the force remains elusive and has yet to be directly detected.

"Dark energy might never reveal its nature," Science staff writer Adrian Cho wrote. "Still, scientists remain optimistic that nature will cooperate and that they can determine the origins of dark energy."

How hot is dark matter? In the 1960s and 1970s, astronomers hypothesized that there might be more mass in the universe than what is visible. Vera Rubin, an astronomer at the Carnegie Institution of Washington, studied the speeds of stars at various locations in galaxies. [ Top 10 Strangest Things in Space ]

Rubin observed that there was virtually no difference in the velocities of stars at the center of a galaxy compared to those farther out. These results seemed to go against basic Newtonian physics, which implies that stars on the outskirts of a galaxy would orbit more slowly.

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