A giant cloud of hydrogen gas is heading for a collision with our Milky Way Galaxy, and when it hits, it may set off a spectacular burst of stellar fireworks. The cloud, called Smith’s Cloud after the astronomer who discovered it, is 11,000 light-years long and 2,500 light-years wide and has enough hydrogen to make a million or so stars the size of the Sun. It’s only 8,000 light-years from our Galaxy’s disk and coming in at about 250 km/s. Don’t panic! It will hit 30,000 light years away from Earth—about 40 million years from now.
This 360-degree panorama covers all of the southern and northern celestial hemispheres. The plane of our Milky Way Galaxy, which we see edge-on from Earth, is the luminous band across the image. The projection used in the picture puts the viewer in front of our Galaxy with the Galactic Plane running horizontally through the image. It’s almost as if we were looking at the Milky Way from the outside because the solar system is near the galactic rim. From our vantage point the general components of our spiral galaxy come clearly into view, including its disc as well as the central bulge and nearby satellite galaxies.
Over next couple of billion years, these two spiral galaxies will end up in a complete galactic merger—the two galaxies will become a single, larger one. They’re about 150 million light-years away in the constellation of Canis Major (the Great Dog), so what we can see now is what was happening 150 million years ago.
The gravitational attraction of NGC 2207, the larger of the pair, is already stirring things up throughout its smaller partner, distorting IC 2163’s shape and throwing stars and gas into long streamers that extend over 100,000 light-years. However, most of the space between stars in a galaxy is empty. When these galaxies collide, almost none of the stars in them will crash into another star.
This 150 million old image is a vision of the Milky Way’s future. About the time NGC 2207 and IC 2163 have finished their merger, the Milky Way will begin colliding with the Andromeda Galaxy.
G1.9+0.3 is the remnant of the most recent supernova in our galaxy. It is estimated to have occurred about 110 years ago in a dusty region of the galaxy that blocked visible light from reaching Earth, but it can be seen by x-ray telescopes such as Chandra X-ray Observatory.
Here is ESA’s explanation of this video—This video reveals the changing face of our Galaxy, tracing the motion of two million stars five million years into the future using data from the Tycho-Gaia Astrometric Solution, one of the products of the first Gaia data release. This provides a preview of the stellar motions that will be revealed in Gaia’s future data releases, which will enable scientists to investigate the formation history of our Galaxy.
The stars are plotted in Galactic coordinates and using a rectangular projection: in this, the plane of the Milky Way stands out as the horizontal band with greater density of stars.
The video starts from the positions of stars as measured by Gaia between 2014 and 2015, and shows how these positions are expected to evolve. The frames in the video are separated by 750 years, and the overall sequence covers five million years. The stripes visible in the early frames reflect the way Gaia scans the sky and the preliminary nature of the first data release; these artefacts are gradually washed out in the video as stars move across the sky.
The shape of the Orion constellation can be spotted towards the right edge of the frame, just below the Galactic Plane, at the beginning of the video. As the sequence proceeds, the familiar shape of this constellation (and others) evolves into a new pattern. Two stellar clusters – groups of stars that were born together and consequently move together – can be seen towards the left edge of the frame: these are the alpha Persei (Per OB3) and Pleiades open clusters.
This video comparison shows the central region of the Milky Way as seen in four different wavelength ranges. As the wavelengths get shorter, some farther objects are obscured.
One view shows compact sources of submillimetre radiation detected by ESO’s APEX as part of the ATLASGAL survey along with complementary data from ESA’s Planck satellite to capture more extended features. A second view shows the region as seen in shorter, infrared, wavelengths by the Spitzer Space Telescope. Another view shows the same part of sky again at even shorter (near-infrared) wavelengths as seen by ESO’s VISTA infrared survey telescope. Regions appearing as dark dust tendrils here show up brightly in the ATLASGAL view. The fourth view is in visible light, and most of the more distant structures are hidden in that view.