Cassiopeia A
Credit
NASA/CXC/SAO
Where do most of the elements essential for life on Earth come from?
The answer: inside the furnaces of stars and the explosions that mark
the end of some stars' lives.
Astronomers have long studied exploded stars and their remains — known as "supernova remnants" — to better understand exactly how stars produce and then disseminate many of the elements observed on Earth, and in the cosmos at large.
Due to its unique evolutionary status, Cassiopeia A (Cas A) is one of
the most intensely studied of these supernova remnants. A new image
from NASA's Chandra X-ray Observatory shows the location of different
elements in the remains of the explosion: silicon (red), sulfur
(yellow), calcium (green) and iron (purple). Each of these elements
produces X-rays
within narrow energy ranges, allowing maps of their location to be
created. The blast wave from the explosion is seen as the blue outer
ring.
Location of elements in Cassiopeia A.
Credit: NASA/CXC/SAO
X-ray telescopes such as Chandra are important to study supernova
remnants and the elements they produce because these events generate
extremely high temperatures — millions of degrees — even thousands of
years after the explosion. This means that many supernova remnants,
including Cas A, glow most strongly at X-ray wavelengths that are
undetectable with other types of telescopes.
Chandra's sharp X-ray vision allows astronomers to gather detailed
information about the elements that objects like Cas A produce. For
example, they are not only able to identify many of the elements that
are present, but how much of each are being expelled into interstellar
space.
The Chandra data indicate that the supernova that produced Cas A has
churned out prodigious amounts of key cosmic ingredients. Cas A has
dispersed about 10,000 Earth masses worth of sulfur alone, and about
20,000 Earth masses of silicon. The iron in Cas A has the mass of about
70,000 times that of the Earth, and astronomers detect a whopping one
million Earth masses worth of oxygen being ejected into space from Cas
A, equivalent to about three times the mass of the Sun. (Even though
oxygen is the most abundant element in Cas A, its X-ray emission is
spread across a wide range of energies and cannot be isolated in this
image, unlike with the other elements that are shown.)
Astronomers have found other elements in Cas A in addition to the
ones shown in this new Chandra image. Carbon, nitrogen, phosphorus and
hydrogen have also been detected using various telescopes that observe
different parts of the electromagnetic spectrum. Combined with the
detection of oxygen, this means all of the elements needed to make DNA,
the molecule that carries genetic information, are found in Cas A.
Periodic Table of Elements
Credit: NASA/CXC/K. Divona
Oxygen is the most abundant element in the human body
(about 65% by mass), calcium helps form and maintain healthy bones and
teeth, and iron is a vital part of red blood cells that carry oxygen
through the body. All of the oxygen in the Solar System comes from exploding massive stars.
About half of the calcium and about 40% of the iron also come from
these explosions, with the balance of these elements being supplied by
explosions of smaller mass, white dwarf stars.
While the exact date is not confirmed (PDF),
many experts think that the stellar explosion that created Cas A
occurred around the year 1680 in Earth's timeframe. Astronomers estimate
that the doomed star was about five times the mass of the Sun just
before it exploded. The star is estimated to have started its life with a
mass about 16 times that of the Sun, and lost roughly two-thirds of
this mass in a vigorous wind blowing off the star several hundred
thousand years before the explosion.
Earlier in its lifetime, the star began fusing hydrogen and helium in
its core into heavier elements through the process known as "nucleosynthesis."
The energy made by the fusion of heavier and heavier elements balanced
the star against the force of gravity. These reactions continued until
they formed iron in the core of the star. At this point, further
nucleosynthesis would consume rather than produce energy, so gravity
then caused the star to implode and form a dense stellar core known as a
neutron star.
Pre-Supernova Star:
As it nears the end of its evolution, heavy elements produced by nuclear
fusion inside the star are concentrated toward the center of the star.
Illustration Credit: NASA/CXC/S. Lee
Chandra has repeatedly observed Cas A since the telescope was launched into space in 1999. The different datasets have revealed new information about the neutron star in Cas A, the details of the explosion, and specifics of how the debris is ejected into space.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Fast Facts for Cassiopeia A:
Scale: Image is 8.91 arcmin across (about 29 light years)
Category: Supernovas & Supernova Remnants
Observation Date: 16 pointings between Jan. 2000-Nov. 2010
Observation Time: 353 hours (14 days, 17 hours)
Obs. ID: 114, 1952, 4634-4639, 5196, 5319, 5320, 6690, 10935, 10936, 12020, 13177
Instrument: ACIS
Also Known As: Cas A
References: Hwang and Laming, 2012, ApJ, 746, 130; arXiv:1111.7316; Lee, et al. 2014, ApJ, 789, 7; arXiv:1304.3973
Color Code: X-rays: Red: Silicon, Yellow: Sulphur, Green: Calcium, Purple: Iron, Blue: Blast Wave
Distance Estimate: About 11,000 light years
Source: NASA’s Chandra X-ray Observatory
