The Wonder of It All

Courtesy of KIPAC

The universe has been around for roughly 13.7 billion years, but it still holds many mysteries that continue to perplex astronomers to this day. Ranging from dark energy to cosmic rays to the uniqueness of our own solar system, there is no shortage of cosmic oddities.



The journal Science summarized some of the most bewildering questions being asked by leading astronomers today. In no particular order, here are eight of the most enduring mysteries in astronomy:

FIRST STOP: Dark Energy

What is Dark Energy?

NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM)

Dark energy is thought to be the enigmatic force that is pulling the cosmos apart at ever-increasing speeds, and is used by astronomers to explain the universe's accelerated expansion.



This elusive force has yet to be directly detected, but dark energy is thought to make up roughly 73 percent of the universe.

NEXT STOP: Dark Matter

How Hot is Dark Matter?

ESO/L. Calçada

Dark matter is an invisible mass that is thought to make up about 23 percent of the universe. Dark matter has mass but cannot be seen, so scientists infer its presence based on the gravitational pull it exerts on regular matter.



Researchers remain curious about the properties of dark matter, such as whether it is icy cold as many theories predict, or if it is warmer.

NEXT UP: Missing Baryons

Where are the Missing Baryons?

Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang Illustration: CXC/M. Weiss

Dark energy and dark matter combine to occupy approximately 95 percent of the universe, with regular matter making up the remaining 5 percent. But, researchers have been puzzled to find that more than half of this regular matter is missing.



This missing matter is called baryonic matter, and it is composed of particles such as protons and electrons that make up majority of the mass of the universe's visible matter.



Some astrophysicists suspect that missing baryonic matter may be found between galaxies, in material known as warm-hot intergalactic medium, but the universe's missing baryons remain a hotly debated topic.

NEXT UP: Supernova Explosions

How do Stars Explode?

A. Ravasio (LULI), A. Pelka (LULI), J. Meinecke (Oxford) and C. Murphy (Oxford)/ F. Miniati (ETH).

When massive stars run out of fuel, they end their lives in gigantic explosions called supernovas. These spectacular blasts are so bright they can briefly outshine entire galaxies.



Extensive research and modern technologies have illuminated many details about supernovas, but how these massive explosions occur is still a mystery.



Scientists are keen to understand the mechanics of these stellar blasts, including what happens inside a star before it ignites as a supernova.

NEXT UP: Re-ionization of the Universe

What Re-ionized the Universe?

ESO/M. Kornmesser

The broadly accepted Big Bang model for the origin of the universe states that the cosmos began as a hot, dense point approximately 13.7 billion years ago.



The early universe is thought to have been a dynamic place, and about 13 billion years ago, it underwent a so-called age of re-ionization. During this period, the universe's fog of hydrogen gas was clearing and becoming translucent to ultraviolet light for the first time.



Scientists have long been puzzled over what caused this re-ionization to occur.

NEXT UP: Cosmic Rays

What's the Source of the Most Energetic Cosmic Rays?

NSF/J. Yang

Cosmic rays are highly energetic particles that flow into our solar system from deep in outer space, but the actual origin of these charged subatomic particles has perplexed astronomers for about a century.



The most energetic cosmic rays are extraordinarily strong, with energies up to 100 million times greater than particles that have been produced in manmade colliders. Over the years, astronomers have attempted to explain where cosmic rays originate before flowing into the solar system, but their source has proven to be an enduring astronomical mystery.

NEXT UP: Our Solar System

Why is the Solar System so Bizarre?

SPACE.com

As alien planets around other stars are discovered, astronomers have tried to tackle and understand how our own solar system came to be.



The differences in the planets within our solar system have no easy explanation, and scientists are studying how planets are formed in hopes of better grasping the unique characteristics of our solar system.



This research could, in fact, get a boost from the hunt for alien worlds, some astronomers have said, particularly if patterns arise in their observations of extrasolar planetary systems.

NEXT UP: The Sun's Corona

Why is the Sun's Corona so Hot?

NASA/SDO/AIA

The sun's corona is its ultra-hot outer atmosphere, where temperatures can reach up to a staggering 10.8 million degrees Fahrenheit (6 million degrees Celsius).



Solar physicists have been puzzled by how the sun reheats its corona, but research points to a link between energy beneath the visible surface, and processes in the sun's magnetic field. But, the detailed mechanics behind coronal heating are still unknown.