Sagittarius Dwarf Spheroidal Galaxy

A tiny group of stars is near us.

It is a small galaxy. It moves in a big loop around our galaxy. The big galaxy is pulling the small one apart. This happens because of a strong pull.

This pull can make new stars grow. The small galaxy is very old. It has many groups of stars inside it. It is slowly joining our big galaxy. This will take a very long time.

The Sagittarius Dwarf Spheroidal Galaxy is a small galaxy. It is a neighbor to our Milky Way.

This galaxy has a loop shape. It travels in a polar orbit. This means it moves over the Milky Way's poles. It is about 70,000 light-years from Earth. It is also 50,000 light-years from the Milky Way's core.

Inside this small galaxy are many star groups. We call these groups globular clusters. One large cluster is named M54. It sits at the core.

The Milky Way is much bigger. It is 10,000 times more massive. Because of this, the Milky Way pulls on the small galaxy. This pull is called tidal force. These forces are tearing the small galaxy apart. It is slowly joining our galaxy. This process will take a billion years.

Scientists found that this galaxy helps our home. Its movements can cause ripples in stars. These ripples happen near the Milky Way's core. Some studies say these hits helped make our galaxy's spiral shape. It may even help make new stars form.

The Sagittarius Dwarf Spheroidal Galaxy is a small neighbor to our Milky Way. It is shaped like a loop and moves in a polar orbit. This means it travels over the poles of our galaxy.

The galaxy is about 10,000 light-years across. It sits roughly 70,000 light-years away from Earth. It stays about 50,000 light-years from the Milky Way's core. This makes it a close companion to our home galaxy.

This small galaxy is being pulled apart by huge tidal forces. These forces come from the Milky Way, which is 10,000 times more massive. As the dwarf galaxy moves, it leaves behind long stellar streams of stars.

The main cluster will pass through the Milky Way's disc soon. This will happen within the next hundred million years. Scientists think the two galaxies will fully merge in one billion years. This slow process is how the smaller galaxy is absorbed.

Astronomers officially discovered this galaxy in 1994. Rodrigo Ibata, Mike Irwin, and Gerry Gilmore found it. At that time, it was the nearest neighbor known to us.

Later, in 2003, Steven Majewski, Michael Skrutskie, and Martin Weinberg used infrared data. They used supercomputers to map its full loop shape. This helped them see the galaxy through many background stars. They found it sits at a near right angle to our galaxy.

Inside the galaxy, you can find many globular clusters. These are large groups of stars. One bright group is called M54, and it sits at the core.

Other clusters like Terzan 7 and Terzan 8 are also in the main body. Some clusters, like Palomar 12, are found in the outer streams. While scientists once thought there were few clusters, new data shows at least twenty more. These newer clusters have more metal than the older ones.

This galaxy helps us understand how the Milky Way works. In 2018, the Gaia project showed the dwarf galaxy caused ripples in stars. These ripples happened when it passed the Milky Way's core long ago.

Some studies suggest these collisions helped create our galaxy's spiral shape. These hits may have even triggered the birth of new stars. It is amazing to think a small neighbor can change a huge galaxy.

The Sagittarius Dwarf Spheroidal Galaxy, or Sgr dSph, is a satellite galaxy of the Milky Way. It is an elliptical, loop-shaped structure that orbits our home galaxy. This galaxy is important because it shows how large galaxies grow by absorbing smaller ones. Sgr dSph is currently about 70,000 light-years away from Earth. It stays roughly 50,000 light-years from the core of the Milky Way. This distance is only about one third of the distance to the Large Magellanic Cloud.

The galaxy moves in a polar orbit. This means its path takes it over the galactic poles of the Milky Way. As it travels, it is being pulled apart by immense tidal forces. These forces are caused by the massive gravity of the Milky Way. The Milky Way is about 10,000 times more massive than Sgr dSph. This gravitational pull is slowly tearing the dwarf galaxy into long stellar streams. These streams are paths of stars ripped out from the dwarf galaxy. The main cluster is expected to pass through the Milky Way's galactic disc within the next 100 million years. Scientists calculate that the merger will be complete in about one billion years.

Sgr dSph contains many globular clusters, which are dense groups of stars. The brightest cluster is Messier 54, or M54, which sits at the galaxy's core.

Other clusters located in the main body include Terzan 7, Terzan 8, and Arp 2. Some clusters, such as Palomar 12 and Whiting 1, are found in the extended stellar streams. While astronomers once thought the galaxy had few clusters, new data from VVV and Gaia EDR3 suggests there are at least twenty more. These newer clusters are more metal-rich than the older ones. This variety shows that the galaxy has many different stellar populations.

The history of discovering this galaxy began in 1994. Astronomers Rodrigo Ibata, Mike Irwin, and Gerry Gilmore officially identified it. At the time, it was recognized as the nearest known neighbor to the Milky Way. In 2003, researchers Steven Majewski, Michael Skrutskie, and Martin Weinberg used infrared telescopes and supercomputers to map the galaxy. They used 2MASS Two-Micron All Sky Infrared Survey data to see the full loop shape. This helped them distinguish the dwarf galaxy from the mass of background stars. They found the galaxy sits at a near right angle to the plane of the Milky Way.

Scientists study the metallicity of the galaxy to understand its age. Metallicity refers to the amount of elements heavier than hydrogen and helium in a star. Sgr dSph has an age-metallicity relationship. Its oldest populations are metal-poor, meaning they have very few heavy elements. Its youngest populations have super-solar abundances, meaning they have more heavy elements than our Sun. A 2019 study by Matthew Melendez showed that metallicity decreases as you move away from the core. There is also a larger spread of metallicity in the core compared to the outer regions.

Observations have shown that Sgr dSph has a powerful effect on the Milky Way. In 2018, the European Space Agency's Gaia project revealed that the dwarf galaxy caused perturbations in stars near our galactic core. These are rippling movements in the stars triggered when Sgr dSph passed through the Milky Way between 300 and 900 million years ago. Some simulations from 2011 suggest these repeated collisions may have helped the Milky Way develop its spiral structure. Additionally, a 2020 study concluded that these collisions triggered major episodes of star formation in the Milky Way.

The movement of Sgr dSph is complex and continues to be studied. Some astronomers believe the galaxy has orbited the Milky Way for billions of years. They suggest it may have completed about ten orbits already. If this is true, the galaxy must have a high concentration of dark matter to stay together despite the tidal strain. In 1999, researchers concluded that its mass had decreased by a factor of two or three during its orbit. Current studies, including the MilkyWay@Home project, use computational support to better understand its path and the debris it leaves behind.