View Full Version : Discussion: Hotspot Found On Geminga

2004-Jul-19, 03:54 PM
SUMMARY: Astronomers have detected a small bright spot on a familiar neutron star, Geminga, located 500 light-years away. The hot spot was discovered using the XMM-Newton x-ray observatory, and it's the size of a football field. Geminga itself is only 20 km (12.4 miles) across, and spins 4 times a second, but it's got 1.5 times the mass of our own Sun. The hot spot is created because material ejected from the rapidly spinning object is being recaptured by its gravity, and then funneled by its magnetic field to strike a specific point, heating it up millions of degrees.

What do you think about this story? Post your comments below.

2004-Jul-19, 04:52 PM
wow amazing that they can find something like this so far away

2004-Jul-19, 05:39 PM
The hot-spot on Geminga has been debated in various threads on this forum previously. For me it is an interesting detail in our further understanding of old neutron stars.

Rich Faulkner
2004-Jul-19, 09:44 PM
Question: Regarding the pix with the article: I gather that the pix is the actual star? If so, where is the hot spot? Can you reissue the pix with a circle around the hotspot? If it's the actual hotspot on the surface of the star (the background in the pix?) that is incredible! In this scenerio, I'd still be curious to see the hot spot relative to the star.

2004-Jul-20, 12:00 AM
Originally posted by Rich Faulkner@Jul 19 2004, 09:44 PM
I gather that the pix is the actual star?
No, the image that goes with this picture is showing what would effectively be the heliopause around Geminga as it goes through its local interstellar media. Geminga itself is about one millionth of a pixel across in the center.

Geminga is 500 light years away. which is about 5 quadrillion kilometers from here. Geminga is about 20 kilometers across. The hotspot is about 100 meters across. To directly image the hotspot in 0.1 nanometer hard xrays would require an xray telescope with an aparature of about 50,000 kilometers. We won't be building that very soon.

The methods used to observe this spot have to do with measuring the spectrum and intensity of the light, and using the Hubble measured parallax distance to the object. The team got a lot of viewing time with XMM Newton and binned the counts according to where they fit into the 230 milliscond rotational period of Geminga. From this they could tell the size of the hotspot.

Here's a link to an easy-to-read paper the team posted today on this topic:
PHASE-RESOLVED SPECTROSCOPY OF GEMINGA SHOWS ROTATING HOT SPOT(S) (http://www.arxiv.org/ftp/astro-ph/papers/0407/0407402.pdf)

Rich Faulkner
2004-Jul-20, 02:33 PM
Ah, that explains it! (That may sound funny, but it really does. It was more of a discovery based on reading the data as opposed to someone "eyeballing it". ) Thanks for clearing that up and thanks for the link. I guess you don't have to draw a circle around the pixel. ;)