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Cepheus B: Trigger-Happy Star Formation
Cepheus B
Cepheus B

  • Cepheus B is a cloud of molecular hydrogen, a place where stars are known to form

  • Researchers used Chandra and Spitzer to study this cloud, which is relatively close at 2,400 light years away

  • The combined data reveal that massive stars may trigger star formation more often than previously thought

This composite image, combining data from the Chandra X-ray Observatory and the Spitzer Space Telescope shows the molecular cloud Cepheus B, located in our Galaxy about 2,400 light years from the Earth. A molecular cloud is a region containing cool interstellar gas and dust left over from the formation of the galaxy and mostly contains molecular hydrogen. The Spitzer data, in red, green and blue shows the molecular cloud (in the bottom part of the image) plus young stars in and around Cepheus B, and the Chandra data in violet shows the young stars in the field.

The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission. The Spitzer data showed whether the young stars have a so-called "protoplanetary" disk around them. Such disks only exist in very young systems where planets are still forming, so their presence is an indication of the age of a star system.

These data provide an excellent opportunity to test a model for how stars form. The new study suggests that star formation in Cepheus B is mainly triggered by radiation from one bright, massive star (HD 217086) outside the molecular cloud. According to the particular model of triggered star formation that was tested -- called the radiation-driven implosion (RDI) model -- radiation from this massive star drives a compression wave into the cloud triggering star formation in the interior, while evaporating the cloud's outer layers.

The labeled version of the image (rollover the image above) shows important regions in and around Cepheus B. The "inner layer" shows the Cepheus B region itself, where the stars are mostly about one million years old and about 70-80% of them have protoplanetary disks. The "intermediate layer" shows the area immediately next to Cepheus B, where the stars are two to three million years old and about 60% of them have disks, while in the "outer layer" the stars are about three to five million years old and about 30% of them have disks. This increase in age as the stars are further away from Cepheus B is exactly what is predicted from the RDI model of triggered star formation.

Different types of triggered star formation have been observed in other environments. For example, the formation of our solar system was thought to have been triggered by a supernova explosion, In the star-forming region W5, a "collect-and-collapse" mechanism is thought to apply, where shock fronts generated by massive stars sweep up material as they progress outwards. Eventually the accumulated gas becomes dense enough to collapse and form hundreds of stars. The RDI mechanism is also thought to be responsible for the formation of dozens of stars in W5. The main cause of star formation that does not involve triggering is where a cloud of gas cools, gravity gets the upper hand, and the cloud falls in on itself.

Fast Facts for Cepheus B:
Credit  X-ray (NASA/CXC/PSU/K. Getman et al.); IR (NASA/JPL-Caltech/CfA/J. Wang et al.)
Release Date  August 12, 2009
Scale  Image is 15 arcmin across
Category  Normal Stars & Star Clusters, White Dwarfs & Planetary Nebulas
Coordinates (J2000)  RA 22h 56m 46.99s | Dec +62° 40' 0.0012"
Constellation  Cepheus
Observation Date  03/11/2003
Observation Time  8 hours
Obs. ID  3502
Instrument  ACIS
References Getman, K.V., et al. (2009), ApJ, 699, 1454
Color Code  X-ray (Violet); IR (Red, Green, Blue)
Distance Estimate  About 2400 light years
distance arrow
Visitor Comments (9)

Excellent explanation, and terminology Thank you. Sincerely

Posted by Arhtur H. Nittolo on Tuesday, 09.9.14 @ 02:12am

What you write here is quite interesting I'll check your posts more often.

Posted by Marianne on Wednesday, 11.17.10 @ 12:31pm

I am not aware of observations of Hafnium in interstellar gas. An interesting point is that it's been recently reported that if even a tiny amount of a certain isotope of Hafnium was found on Earth it would show that a supernova once exploded near our solar system.

Posted by annunci on Thursday, 05.27.10 @ 11:03am

Dear Ben,
I am not aware of observations of Hafnium in interstellar gas. An interesting point is that it's been recently reported that if even a tiny amount of a certain isotope of Hafnium was found on Earth it would show that a supernova once exploded near our solar system.

P. Edmonds, CXC

Posted by P. Edmonds on Monday, 09.14.09 @ 14:58pm

Dear Herman,
This depends on your reference point. By cosmic standards 2400 light years is indeed close, since the Universe is billions of light years across.
By human standards 10 yards is a short distance, but for an ant it's a long journey. I don't think this is a "distortion" of our human perception, but rather an expansion of it.

P. Edmonds, CXC

Posted by P. Edmonds on Monday, 09.14.09 @ 14:56pm

Does the interstellar gas contain any HF?

Posted by ben on Tuesday, 08.18.09 @ 22:32pm

I'm still bothered by 2400 light years away as somehow being close to us. Distances immensities etc seem so out of my mental touch. My corner drugstore is six miles away and that seems far to me. How can we avoid tossing off huge distances and thereby distorting our simple human perception of things?

Posted by Herman Cole on Saturday, 08.15.09 @ 12:33pm

It's amazing.
Thank you for showing the illustration.

Posted by Suatmaji on Friday, 08.14.09 @ 23:20pm

What direction are these coordinates?

Posted by joanne piluso on Wednesday, 08.12.09 @ 18:22pm

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