Astronomical discoveries in 2012 have reshaped what we know about the universe and pushed some instruments to the very limits of their observing power.

Scientists discovered a galaxy that harbors an enormous central black hole 17 billion times more massive than the sun. Another research group spotted a scorching-hot rocky planet in the closest star system to our own. Meanwhile, the records for most massive galaxy cluster and most distant galaxy were shattered.

Here's a brief rundown of some of the year's most extreme and exciting cosmic finds.

Most monstrous black hole

Observers probably don't want to get too close to NGC 1277 or its supermassive black hole, which takes up a large portion of the galaxy itself. The central black hole is 17 billion times more massive than the sun and makes up 14 percent of its host galaxy's mass, compared to the usual 0.1 percent.

Researchers were so flummoxed by the black hole's size that they took an extra year to double-check their calculations before publishing their results.

Closest exoplanet to Earth

In a surprise discovery, astronomers found a planet that is about the same size as Earthin the star system next door. The rocky planet was found in Alpha Centauri, a three-star system just 4.3 light years from us. [Alpha Centauri Planet and Stars Explained (Infographic)]

Life is very unlikely on this world. Its rocky surface may be molten, since the planet orbits just 3.6 million miles (6 million kilometers) from its sun-like star. (Earth, for comparison, circles 93 million miles, or 150 million km, from the sun).

Alpha Centauri Bb, as the planet is known, was discovered through tracking gravitational wobbles around its planet star. The wobbles in this case are very subtle, making the star move back and forth at no more than 1.1 mph (1.8 kph). The research team stated it "pushed our technique to the limit," and some astronomers are skeptical that the planet even exists.

And just this month, a different research team detected five potential planets orbiting the star Tau Ceti, which lies only 11.9 light-years from Earth. One of the newly spotted candidate worlds may be capable of supporting life as we know it, scientists say.

Artist's impression of five possible planets orbiting the star Tau Ceti, which is just 11.9 light-years from Earth. (Image credit: J. Pinfield for the RoPACS network at the University of Hertfordshire, 2012.)

Smallest alien worlds

Astronomers using NASA's Kepler Space Telescope discovered three tiny planets 120 light-years away from Earth. Circling the star KOI-961, the smallest of the three planets is about the size of Mars, and all are smaller than Earth. Even the star itself is tiny — just 70 percent larger than Jupiter.

"This is the most compact system of planets," said John Johnson, of the California Institute of Technology in Pasadena. "It's like you have a shrink raygun and set it to seven times smaller and zapped a planetary system."

Smallest solar system

KOI-500 has five planets so crowded together that their gravity jostles each other profoundly during their orbits. Their "years" are only 1, 3, 4.6, 7.1 and 9.5 days long. Furthermore, the planets are tiny: just 1.3 to 2.6 times the size of Earth.

All of this action takes place in an area 150 times smaller than Earth's orbit, astronomers said.

"At this rate, you could easily pack in 10 more planets, and they would still all fit comfortably inside the Earth's orbit," Darin Ragozzine, a planetary scientist at the University of Florida at Gainesville, said in a statement.

Most distant galaxy

Much like the 100-meter dash world record, the record for farthest known galaxy often changes. The newest potential record-holderis UDFj-39546284, which had taken shape when the universe was only 380 million years old. Its extreme age was discovered in 2012 using new observations from NASA's Hubble Space Telescope.

The galaxy is part of a group of seven that astronomers examined, forming perhaps the first reliable observations of galaxies that formed 400 million and 600 million years after the Big Bang created the universe 13.7 billion years ago. [Gallery: Spectacular Hubble Photos]

Oldest, most distant supernovas

In 2012, astronomers described what they think led to the oldest, most distant supernovas in the universe. Scientists believe some of these "super-luminous" supernovas come from massive stars — 100 to 250 times the mass of the sun — that explode and blast their matter into space.

Astronomers stated that inside these massive stars, gamma-ray light changes into electron pairs as well as antimatter positrons. The gamma rays usually stop the star from collapsing due to gravity, but the grip weakens as gamma rays convert to matter. It is at this point that the star implodes, sparking the explosion.

Most massive galaxy cluster

At 2,000 times more massive than the Milky Way, a large cluster of galaxies some 7 billion light-years away dwarfs just about any other collection of matter known. Astronomers say the cluster — properly known as SPT-CLJ2344-4243and dubbed the Phoenix cluster — appears to contain thousands of galaxies of many different sizes.

Astronomers first spotted the Phoenix cluster in 2010, but didn't realize its extent until they did follow-up observations with NASA's Chandra X-ray Observatory. High-energy light pouring out of the cluster make it the most X-ray luminous one ever found, at 35 percent brighter than the last record-holder found.

Biggest map of the universe

Courtesy of a mega map, astronomers are a step closer to understanding how the universe came to be. The Sloan Digital Sky Survey III released a map that charts more than 1 million galaxies in a total volume of 70 billion cubic light-years.

The map could help astronomers better understand the mysterious dark matter and dark energy that appears to make up most of the universe, researchers said.

Deepest view of the universe

The Hubble Space Telescope is peering back further and further in time. The famous orbiting observatory captured light that emanated 13.2 billion years ago, when the universe was just 500 million years old or so.

Hubble's picture, which is called the eXtreme Deep Field, shows galaxies and starlight accumulated over 10 years in a small bit of sky; this is the best method we have to see objects so far away. The photo is a successor to Hubble's "Ultra Deep Field", which the telescope took in 2003 and 2004. [Video: Hubble's eXtreme Deep Field]

Most magnetic star

There's a star 20,000 light-years from Earth with a real magnetic personality. NGC 1624-2, which is about 35 times as massive as our sun, was spotted in the constellation Perseus. With a magnetic field 20,000 times stronger than the sun's— and 10 times more powerful than that of any known star — NGC 1624-2 drags a blanket of trapped charged particles around it.

"Magnetic fields of this strength are extremely rare; they are only known to exist in a few other stars of much lower mass," study lead author Gregg Wade, an astronomer at the Royal Military College of Canada, told SPACE.com in a September interview. "To find such a strong field is very lucky."

X-ray blast in the universe's youth

A jet of X-rays emanating from quasar GB 1428 — a galaxy that has a huge black hole in its center — was found about 12.4 billion light-years from Earth. The radiation band is estimated at about twice the diameter of the Milky Way.

With the previous record-holder at 12.2 billion light-years away, astronomers said they are getting more information on how black holes behaved in the universe's early days.

Biggest core found in a ginormous galaxy

Lurking in a galaxy about 10 times the width of the Milky Way lies a large, diverse galactic core that doesn't seem to have a black hole associated with it.

The wispy core of A2261-BCG, which is about 10,000 light-years across, puzzles astronomers because supermassive black holes are expected to be at the heart of most galaxies. Hubble Space Telescope observations suggest the core might have been constructed when two galaxies merged.

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