Looking deep inside the Orion Nebula, the Hubble Space Telescope has captured a stunning collection of protoplanetary disks – or proplyds – which are embryonic solar systems in the making. Using Hubble’s Advanced Camera for Surveys (ACS), researchers have discovered 42 protoplanetary blobs, which are being illuminated by a bright star cluster. These disks, which sometimes appear like boomerangs, arrows, or space jellyfish, surround baby stars and are shedding light on the mechanism behind planet formation.
As newborn stars emerge from the nebula’s mixture of gas and dust, proplyds form around them. The center of the spinning disc heats up and becomes a new star, but remnants around the outskirts of the disc attract other bits of dust and clump together. This is the beginning of a solar system.
But not all proplyds face a bright and happy future, even in these beautiful images.
Bright star that illuminates some of the proplyds is both a blessing and a curse. The disks that lie close to the brightest star in the cluster (Theta 1 Orionis C) are being zapped by the star’s powerful emissions. The radiation that lights them up and makes them visible also threatens their very existence. As the disk material begins to heat, it is very likely to dissipate and dissolve, destroying the potential for planets to form. Some of these proplyds will be torn apart; however others will survive and perhaps evolve into planetary systems.
Discs that are farther away do not receive enough energetic radiation from the star to heat up the gas and so they can only be detected as dark silhouettes against the background of the bright nebula, as the dust that surrounds these discs absorbs background visible light. By studying these silhouetted discs, astronomers are better able to characterize the properties of the dust grains that are thought to bind together and possibly form planets like our own.
The brighter discs are indicated by a glowing cusp in the excited material and facing the bright star, but which we see at a random orientation within the nebula, so some appear edge on, and others face on, for instance. Other interesting features enhance the look of these captivating objects, such as emerging jets of matter and shock waves.
It is rare to see proplyds in visible light, but the astronomers were able to use Hubble for this ambitious survey of the familiar and photogenic Orion Nebula.
Protoplanets are small celestial objects that are the size of a moon or a bit bigger. They are small planets, like an even smaller version of a dwarf planet. Astronomers believe that these objects form during the creation of a solar system.
The most popular theory of how a solar system is formed says that a giant cloud of molecular dust collapsed, forming one or more stars. Then a cloud of gas forms around the new star. As a result of gravity and other forces, the dust and other particles in this cloud collide and stick together forming larger masses. While some of these objects break apart on impact, a number of them continue to grow. Once they reach a certain size – around a kilometer – these objects are large enough to attract particles and other small objects with their gravity. They continue to get larger until they form protoplanets. Some protoplanets continue colliding and growing until they form planets while others stay that size.
As the protoplanets grew to become planets, parts of them melted due to radioactivity, gravitational influences, and collisions. Where the objects had melted, the composition of the planets changed. Heavier elements sank, forming the cores of the planets, and lighter objects rose to the surface. This process is called planetary differentiation and explains why planets have heavy cores. Astronomers have discovered that even some asteroids have differentiated, so their cores are heavier than their surfaces.
Protoplanets used to be highly radioactive due to how they were formed. However, over thousands of years, the radioactivity of these objects has greatly decreased because of radioactive decay. Astronomers are still discovering new protoplanets, and most likely, they will discover many more. With better technology, astronomers are now able to find protoplanets in other star systems. Last year, scientists discovered a protoplanet HL Tau b that will probably turn into an actual planet one day. Astronomers say that will not happen for about a million years though because the protoplanet’s star is also very young. In its final form, HL Tau b will look like Jupiter – a gas giant around the same size as that massive planet. It is hard to believe that thousands of years ago our planets were objects about the size of a moon, which were slowly evolving and growing. Astronomers continue to study protoplanets, the same way they study planetesimals, to find out more about how the Solar System was formed.