STARS AND NEBULAs (origin)

Stars are born in clouds of gas and dust. One such stellar nursery is the Orion Nebula, an enormous cloud of gas and dust many light-years across. Turbulence from deep within these clouds creates high density regions called knots. These knots contain sufficient mass that the gas and dust can begin to collapse from gravitational attraction. As it collapses, pressure from gravity causes the material at the center to heat up, creating a protostar. One day, this core becomes hot enough to ignite fusion and a star is born.

Not all of the material in the collapsing cloud ends up as part of a star — the remaining dust can become planets, asteroids or comets … or it may remain as dust. Scientists running three-dimensional computer models of star formation predict that the spinning clouds of collapsing gas and dust may break up into two or three distinct blobs. This would explain why the majority the stars in the Milky Way are paired or in groups of multiple stars.

The chemical makeup of stars, revealed through spectroscopy, depends on the material in which they originate. In the early universe, stars were formed from matter that lacked most elements except for hydrogen and helium. The other chemical elements have been and still are being created in the interior of stars through nuclear fusion processes. That new material is eventually recycled into subsequent generations of stars and planets.

STAR CLUSTERS

Are Stars Born in Groups?Most stars form in multiple star systems, though this formation process is not completely understood. The groupings of stars that form together can vary from a few stars to many hundreds or thousands. The stars in each cluster have a variety of masses. The most massive stars are rare, while the least massive stars are the most numerous.

Hubble has probed star clusters of all sizes and uses spectroscopy to determine the detailed chemistry in star cluster members. By taking precise observations of star cluster members, scientists using Hubble can determine their luminosities (intrinsic brightnesses) and temperatures. This helps refine our understanding of star formation, stellar evolution and the physics of the theoretical models used to explain these phenomena.

The most massive star clusters, containing tens and hundreds of thousands of stars, were mostly formed early on in the universe, about 13 billion years ago. These massive clusters, called globular clusters, persist today although the stars in them have evolved over time. Cluster characteristics are tracers of the earliest times of cosmic star formation. Hubble observations have revealed subtle differences in globular clusters, their chemistry and, in some cases, evidence that these clusters actually have multiple generations of stars within them.

STELLAR DEATH

How Do Stars Die?

When their nuclear fuel is exhausted, the most massive stars explode in a spectacular fashion, called a supernova, leaving behind neutron stars, black holes or nothing at all.

The last time astronomers observed a supernova in our galaxy was in the 1600s. But in 1987, the light from a supernova in one of the Milky Way’s satellite galaxies, the Large Magellanic Cloud, reached Earth. Three years later, Hubble began to monitor the explosion — called Supernova 1987A — from the first-ever ringside seat for a supernova.

Hubble has observed the nebula remnant of Supernova 1987A repeatedly, witnessing rings and knots of gas brightening around the exploded star. Watching the supernova in progress for decades has led to a greater understanding of how these events play out over thousands of years.

Smaller stars like our sun end their lives by ejecting their outer layers of gas into space over the course of about 10,000 years, leaving behind the star’s hot core — a white dwarf. Radiation from the white dwarf causes the gas to glow, creating a unique and beautiful formation called a planetary nebula. The name comes from the early days of astronomy, when observers thought the dim forms they saw through their telescopes might be related to planets.

Hubble’s observations show that planetary nebulas are formed in multiple outbursts, not just in one dying breath, since we can see the previously released material interacting with newly ejected material. Today, Hubble has observed many of these nebulas and found a wide range of complicated and extraordinary shapes, from tunnels to interlocking rings. The Cat's Eye Nebula, for example, consists of 11 bubbles of gas. The Helix Nebula looks like a giant eye staring at us through space. The Red Rectangle — one of the weirdest planetary nebulas of all — appears exactly as sounds.