How many solar systems are there in the milky way?

The galactic center is an intense radio source known as Sagittarius A*, a supermassive black hole of 4,100 (± 0.03 million solar masses. This illustration shows what the surface of TRAPPIST-1f, one of the seven planets in the TRAPPIST-1 system, might look like.

The apex of the Sun’s path, or solar apex, is the direction in which the Sun travels through space in the Milky Way. This is different from the situation within the Solar System, where two-body gravitational dynamics dominate, and different orbits have significantly different velocities associated with them.

Many believe there could be as many as 100 billion different planets in the Milky Way, and there’s even a chance that there’s more than this too. If we then consider all of the other galaxies out there, then all of the solar systems located within these galaxies would be trillions.

But back to our Milky Way – if you consider dwarf planets as part of an other planetary system, there are hundreds of billions of different massive objects in our own Milky Way. And that’s just within our galaxy – there are 2 trillion different galaxies out there, which means that there are many more Earth sized planets outside of the Milky Way too.

Within this flattened (though somewhat warped) disk, the Sun and its planets are embedded in a curved arm of gas and dust, placing the solar system about 26,000 light-years from the galaxy’s turbulent core.

It discovered 17 new planets outside the solar system, or exoplanets, in addition to recovering thousands of known planets. Normally, planets like Earth are more likely to go unnoticed in a planet search than other types because they are so small and orbit so far from their stars. Kepler can only detect planetary systems if they are oriented edge-on to the telescope; otherwise, the instrument will not observe any planetary transits away from the star.

This means that the catalog of planets represents only a small subset of the planets that are actually in orbit around the stars searched for. The team only considered planets orbiting near M dwarfs; their analysis did not include the outer planets of M dwarf systems or worlds orbiting other types of stars. Thus, the researchers calculated the odds that an M dwarf system in the Milky Way would have this orientation, and then combined this with the number of such systems that Kepler is able to detect to arrive at their estimate of 100 billion exoplanets.

Outside the main spiral arms is the Monoceros Ring (or Outer Ring), a ring of gas and stars ripped off from other galaxies billions of years ago. This perception is due, in part, to the fact that observations from Earth are complicated by the fact that the Earth is embedded in the Solar System. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the Solar System lies close to the galactic plane. For more information about the Milky Way, see Hubblesite’s press releases on galaxies, and here’s NASA’s science page on galaxies.

Its extra gravity is normally too weak to alter a star’s trajectory much, but if the star’s orbital velocity matches the speed at which the spiral arm itself is spinning, then the extra force has more time to take effect (Monthly Notices of the Royal Astronomical Society, vol 336, p 78.Outside the main spiral arms is the Monoceros Ring (or Outer Ring), a ring of gas and stars ripped off from other galaxies billions of years ago. Its extra gravity is normally too weak to alter a star’s trajectory much, but if the star’s orbital velocity matches the speed at which the spiral arm itself rotates, then the extra force has more time to take effect (Monthly Notices of the Royal Astronomical Society, vol 336, p 78.According to recent studies, both the Milky Way and the Andromeda Galaxy lie in what is known in the colour-magnitude diagram of galaxies as the green valley, a region populated by galaxies in transition from the blue cloud (galaxies actively forming new stars) to the red sequence (galaxies lacking star formation). Previously, these two galaxies, with 2 e the mass of the Milky Way, were considered too small to influence it. They have to match the right speed, then they are pushed, says Rok Roskar of the University of Zurich (Switzerland).

As the solar system goes around the galaxy, it also swings up and down across the galactic disk about every 60 million years, drifting about 200 light-years to either side. So, basically, if we were to think of the Milky Way as a big disc, we would be the point that’s about halfway between the centre and the edge. And although there was originally a Ninth planet Pluto, it’s now generally accepted that there are only eight planets.

Normally, the interior of the Solar System is protected from the harsh interstellar radiation by the solar wind, a stream of charged particles that flows deep into space, forming a huge electromagnetic shield called the heliosphere. The Solar System (and Earth) lies about 25,000 light-years from the galactic center and 25,000 light-years from the edge.

He found that they are distributed in a sphere about 100,000 light years across, centered at a location in the constellation Sagittarius. As is usual for spiral galaxies, the orbital velocity of most of the stars in the Milky Way does not depend strongly on their distance from the centre.

This occurred at a distance of about 950,000 light-years from the center of the Milky Way, marking the edge of the galaxy, scientists say. The Milky Way is the second largest galaxy in the Local Group (after the Andromeda Galaxy), with its stellar disk about 170,000-200,000 light-years (52-61 kpc) across and, on average, about 1,000 ly (0.3 kpc) thick.

Even in the Andromeda galaxy, which is bright, large, and relatively close to Earth, at 2.3 million light-years only the largest stars and a few variable stars (especially Cepheid variables) are bright enough to shine in telescopes from that distance. On the other hand, there are 64 known stars (of any magnitude, not counting 4 brown dwarfs) within 5 parsecs (16 ly) of the Sun, giving a density of about one star for every 8.2 cubic parsecs, or one for every 284 cubic light years (from the list of nearest stars).

All galaxies are moving away from each other, and their light is shifted towards the red end of the spectrum because this lengthens the wavelengths of light. NGC 7329 (bottom left) is even further away, at a distance of 140 million light years, but it is larger, with a diameter of 140000 light years. Groups of galaxies are grouped into clusters, and clusters into superclusters; superclusters are arranged in huge sheets that stretch across the universe, interspersed with dark voids and giving the whole a kind of spider-web structure. Most of the mass will be made up of dark matter, a type of matter that does not emit light but is thought to make up most of the mass of the universe.

Stars in the innermost 10,000 light-years form a bulge and one or more bars radiating from the bulge. According to the deepest images obtained so far, it is one of the 2 trillion galaxies in the observable universe.

But we now know that some stars are more than three times that distance from the centre of the galaxy, possibly more than four times, so although the Sun hasn’t made any surprising moves, it is much closer to the centre of the galaxy than we thought. The Milky Way is a barred spiral galaxy with a visible diameter estimated to be 100,000-200,000 light years.

With the light-gathering power of this new telescope, it was able to produce astronomical photographs that resolved the outer parts of some spiral nebulae as collections of individual stars. The Milky Way Galaxy is about 1,000,000,000,000,000,000 km (about 100,000 light-years or about 30 kpc) across.

If you look at the outside of the galaxy, you see a central bulge surrounded by four arms, two major and two minor. There are about 208 stars brighter than absolute magnitude 8.5 within a sphere with a radius of 15 parsecs (49 ly) from the Sun, giving a density of one star per 69 cubic parsecs, or one star per 2,360 cubic light years (from the list of nearest bright stars).

From observations, astronomers know that the Milky Way is a barred spiral galaxy about 100,000 light-years across. From Sagittarius, the hazy band of white light appears to pass around the galactic anticenter in Auriga. The halo extends over hundreds of thousands of light-years, much farther than the stellar halo and close to the distance of the Large and Small Magellanic Cloud. A vast halo of dark matter envelops the disk and emits no light, which makes measuring the galaxy’s total size a challenge.