Cassiopeia A facts for kids

Quick facts for kids
Cassiopeia A

This colorful image combines views from three different telescopes. Red shows infrared light (heat) from the Spitzer Space Telescope, gold is visible light from the Hubble Space Telescope, and blue/green is X-ray light from the Chandra X-ray Observatory. The tiny blue dot near the center is what's left of the star's core.
Event type	Supernova
IIb
Date	1947 by Martin Ryle and Francis Graham-Smith)
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Instrument	Lua error in Module:WikidataIB at line 168: attempt to index field 'wikibase' (a nil value).
Constellation	Cassiopeia
Right ascension	23h 23m 24s
Declination	+58° 48.9′
Epoch	J2000
Galactic coordinates	111.734745°, −02.129570°
Distance	c. 11,000 ly
Redshift	Lua error in Module:WikidataIB at line 168: attempt to index field 'wikibase' (a nil value).
Remnant	Shell
Host	Milky Way
Notable features	Strongest radio source beyond the Solar System
Peak apparent magnitude	c. 6
Other designations	Lua error in Module:Wikidata at line 132: attempt to index field 'wikibase' (a nil value).
Preceded by	SN 1604
Followed by	G1.9+0.3 (unobserved, c. 1868), SN 1885A (next observed)

Cassiopeia A (or Cas A) is the glowing remains of a giant star that exploded. This is called a supernova remnant. It is located in the constellation Cassiopeia, about 11,000 light-years away from Earth in our own Milky Way galaxy.

Cas A is special because it's the brightest object in our sky that we can see with radio telescopes, except for our own Sun. The cloud of gas and dust from the explosion is still expanding and is now about 10 light-years wide.

Scientists believe the light from this supernova first reached Earth around the 1660s. However, no one wrote about seeing a bright new star back then. This is likely because clouds of interstellar dust blocked the view, making it hard to see with the eyes.

A Star That No One Saw Explode

By studying how fast the cloud is expanding, astronomers calculated that the explosion should have been visible from Earth around the year 1667. A supernova this close would normally be very bright in the night sky.

One astronomer, John Flamsteed, might have seen it in 1680. He recorded a faint star, but its position in his notes doesn't quite match where Cas A is. It's possible he made a small mistake in his measurements.

Because there are no clear records, it remains a mystery. A bright new star in Cassiopeia would have been visible for months, so it's strange that it was missed. Because of this, no supernova in our Milky Way galaxy has been clearly seen by the naked eye since the invention of the telescope.

An Expanding Cloud of Star Stuff

The shell of material blown off by the star is incredibly hot, about 30 million K. The Kelvin scale is a temperature scale used by scientists. This cloud is also moving at an amazing speed of 4,000 to 6,000 kilometers per second. That's fast enough to travel across the United States in less than a second!

Pictures from the Hubble Space Telescope show that the explosion wasn't a perfect sphere. Instead, it shot out two powerful jets of material in opposite directions. These jets are moving even faster, up to 14,500 km/s. When scientists use colors to map out the different chemical elements in the cloud, they can see that materials from the original star are still grouped together.

Seeing in Radio Waves and X-Rays

Cas A was one of the first objects in space found using radio telescopes, back in 1948. It shines very brightly in radio waves, which are a type of light our eyes cannot see. However, as the remnant cools down over thousands of years, its radio signal is slowly getting weaker by about 1% each year.

Cas A also glows brightly in X-rays, another high-energy form of light. In 1999, the Chandra X-Ray Observatory looked at the center of the remnant. It found a tiny, super-dense object called a neutron star. This is the crushed core of the star that exploded.

A Ghostly Echo of Light

In 2005, the Spitzer Space Telescope saw something amazing: a "light echo" from the supernova. This is like a sound echo, but with light. The bright flash from the explosion traveled through space, bounced off nearby dust clouds, and that reflected light is only now reaching us, centuries later.

By studying the light from this echo, astronomers figured out exactly what kind of star exploded. It was a Type IIb, which comes from a massive star called a red supergiant. This star had already blown away most of its outer hydrogen gas before it finally exploded. This was the first time scientists could study a supernova by its echo, allowing them to look back in time at cosmic events.

A Factory for Life's Building Blocks

Phosphorus is a chemical element that is essential for all life on Earth. It's a key part of our DNA. In 2013, astronomers used telescopes to study the material in Cas A and found large amounts of phosphorus. The amount of phosphorus compared to iron was up to 100 times higher than what is normally found in our galaxy.

This discovery helped prove that supernovae are like cosmic factories. They create heavy elements, including the ones needed for life, and spread them across the galaxy. This material can then form new stars, planets, and maybe even life.

Gallery

See also

• List of supernova remnants
• Light echo