APOD: A Laser Strike at the Galactic Center (2010 Sep 06)

[bystander]

I have a question that pertains to " A Laser Strike at the Galactic Center (2010 Sep 06) " If we were to zoom in on the galactic center with the Hubble at the same time that we are shining the laser at it, we should in theory be able to see the end of the laser beam moving through space towards the galactic center. That's if the theory that light only travels at a certain speed. How long would it take for the laser to reach the center?

The center of the Milky Way is about 25,000 ly away, so it would take 25,000 years for the laser to get there, if it was strong enough and coherent enough to get there at all.

[Chris Peterson]

The center of the Milky Way is about 25,000 ly away, so it would take 25,000 years for the laser to get there, if it was strong enough and coherent enough to get there at all.

The beam loses its coherency quickly- before it even gets out of the Solar System. But the photons will keep heading towards the galactic center, spreading out as they do so. As they encounter regions of dust, most will be absorbed. A very small percentage will ultimately make it, though.

[Chris Peterson]

I have a question That pertains to " A Laser Strike at the Galactic Center (2010 Sep 06) " If we were to zoom in on the galatic center with the hubble at the same time that we are shining the laser at it, we should in theory be able to see the end of the laser beam moving through space twards the galatic center. Thats if the theory that light only travles at a certin speed. How long would it take for the laser to reach the center?

You can't see the beam at all. All you can see is the photons that were in the beam and got scattered back towards the camera. There isn't much to scatter that light in space. Even when it reaches a dust rich area in a few thousand years, it will be so spread out (wider than the Solar System) that we probably couldn't detect any photons. And from our vantage point, Hubble and the laser are so close together that we'd be looking straight up the beam- so there's no way to tell where along its length any scattered light is coming from.

[bystander]

Shooting a Laser at the Galactic Centre
ESO Picture of the Week | potw1045a | 08 Nov 2010

Click to view full size image

This impressive image, taken on 10 May 2010 by ESO astronomer Yuri Beletsky, beautifully depicts the sky above Paranal. One of the 8.2-metre telescopes of ESO's Very Large Telescope, Yepun, Unit Telescope 4, is seen against the wonderful backdrop of the myriad of stars and dust that makes up the Milky Way. A laser beam is coming out of Yepun, aiming perfectly at the Galactic Centre. When used with the adaptive optics system the artificial star created by the beam allows the telescope to obtain images and spectra that are free from the blurring effect of the atmosphere. When this image was taken, astronomers Stefan Gillessen and Hauke Enkel were using the SINFONI instrument, together with the laser guide star facility, to study the centre of our Milky Way, where a supermassive black hole is lurking.

The field of view of the image is very wide, about 180 degrees. One of the 1.8-metre Auxiliary Telescopes used for interferometry can be seen on the right.

Credit: Y. Beletsky/ESO

[neufer]

Click to play embedded YouTube video.

Click to play embedded YouTube video.