My Science School

As their name suggests, dwarf galaxies are smaller galaxies. In contrast to a normal galaxy that comprises hundreds of billions of stars, a dwarf galaxy would contain just about a few billion stars. These dwarf galaxies orbit larger galaxies after their formation.

Formation of dwarf galaxies

The dwarf galaxies are created when two galaxies collide, fromed from the material and dark matter coming out of the galaxies that collided.

Following these collisions, while a significant portion of the gas, dust and stars emitted gets reincorporated into the galaxy created after the collision, some can lead to the formation of dwarf galaxies which then orbit around the galaxy. They are also formed by the gravitational forces existing during the creation of these larger galaxies.

Why are dwarf galaxies crucial

Scientists consider the dwarf galaxies critical as they could help gain insight into the early stages of the formation of galaxies and stars. According to scientists, our galaxy has about 14 satellite dwarf galaxies orbiting it.

Studies are being carried out on these dwarf galaxies as it would give us clues regarding the evolution of the galaxies. By studying the motion of the stars in these galaxies, we would also get to know more about dark matter and how it is distributed in the galaxies.

It is difficult to spot dwarf galaxies as they are less bright when compared to larger galaxies. A large number of them can be spotted in galaxy clusters or as a companion to larger galaxies.

Shapes of dwarf galaxies

The dwarf galaxies take several shapes. The dwarf elliptical galaxies are quite similar to normal elliptical galaxies.

Then there are dwarf spheroidal galaxies which are more spherical in shape and smaller when compared to the former.

Then we have the irregular dwarf galaxies. They do not have a distinct structure and are rich in gas.

One of the closest dwarf galaxies to the Milky Way is the Sagittarius Dwarf Spheroidal Galaxy.

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Now known to host at least 83 moons, researchers propose that Saturn at one point must have had at least one more satellite, which they call Chrysalis

While all four gas giants - Jupiter, Saturn, Uranus, and Neptune - have rings, Saturn is the most popular ringed-planet. Swirling around Saturn's equator, these rings indicate clearly that the planet is spinning at a tilt relative to the plane in which it orbits the sun.

For a long time, astronomers have suspected that this tilt is the result of Saturn's interactions with neighbouring Neptune. A new modelling study by astronomers at Massachusetts Institute of Technology (MIT). however, suggests that while the two planets may have been in sync before, Saturn has since escaped Neptune's pull.

Call it Chrysalis

 In a study appearing in Science in September, the MIT team

posits that a missing moon might be responsible for this planetary realignment. Now known to host at least 83 moons, Saturn at one point must have had at least one more satellite that the researchers call Chrysalis.

The team estimates that after orbiting Saturn for several billion years, Chrysalis became unstable about 160 million years ago, coming too close to Saturn in the process. As the proposed satellite was long dormant before suddenly becoming active - just like a butterfly's chrysalis - the researchers gave it the name Chrysalis.

The resulting encounter pulled the satellite apart and the loss of the moon was enough for Saturn to escape

Neptune's grasp and leave it with its current tilt. Additionally, the researchers suggest that while most of Chrysalis' shattered body may have impacted Saturn, a fraction of its fragments could have remained suspended in orbit. These could then have broken into small icy chunks to form the planet's standout rings.

Explains two mysteries

The missing moon hypothesis, the researchers believe, could thus explain two mysteries pertaining to Saturn's system. While one of these is Saturn's present-day tilt, the other one is the age of its rings.

The rings are estimated to be about 100 million years old. very much younger than the planet itself. If the rings were indeed formed from fragments of Chrysalis, then the story fits perfectly.

Cassini's inputs

The team of researchers arrived at this hypothesis by modelling the interior of Saturn. They identified a distribution of mass that matched the gravitational field that was observed by the Cassini spacecraft in its final phases. What they found indicated that Saturn is no longer in sync with Neptune, paving the way for researching various hypotheses, before arriving at their final result. The lead author of the study says that it is "a pretty good story, but like any other result, it will have to be examined by others".

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Scientists study meteorites for clues about the origin of Earth and the solar system because most meteorites are bits of asteroids that have fallen to Earth, and asteroids are believed to be leftover material from the time the solar system formed.

In 2005, for the first time ever, scientists scooped up rock samples directly from an asteroid using a spacecraft built especially for that purpose. The name of the spacecraft was Hayabusa. It was a robotic spacecraft developed by the Japan Space Exploration Agency (JAXA).

Hayabusa (Japanese for falcon') was launched on May 9, 2003, and arrived in the vicinity of the asteroid Itokawa in mid-September 2005. In November 2005, it landed on the asteroid and collected samples in the form of tiny grains of rock which it brought back to Earth on June 13, 2010. Hayabusa was the first spacecraft to land and take off from an asteroid.

In December 2014, Japan launched another spacecraft Hayabusa 2 to study the near-Earth asteroid Ryugu and to bring back samples of rock not only from its surface but also from deeper below the surface. Hayabusa 2 reached Ryugu in June 2018.

In September 2018, the spacecraft landed two rovers on the asteroid. They were the first rovers ever to move on an asteroid. They moved with a hopping movement instead of rolling around on wheels. The rovers are designed to take pictures of the landscape and measure the temperatures on the asteroid.

Hayabusa 2 left the asteroid in November-December 2019 and delivered a small capsule that contained the rock and dust samples when it was 220,000 km from the Earth's atmosphere. The capsule safely landed in the South Australian outback in December 2020.

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Discovery about an Earth-like planet orbiting an M dwarf could imply that planets orbiting the most common star may be uninhabitable.

Is Earth the only planet that supports life? This is one of the many questions for which we don't have an answer yet. In a universe filled with countless stars and innumerable planets, our quest for life on a planet other than our own continues.

A new discovery could serve as a signpost and maybe even dramatically narrow our search for life on other planets. The discovery, explained in the Astrophysical Journal Letters in October by researchers from the University of California - Riverside, reveals that an Earth-like planet orbiting an M dwarf appears to have no atmosphere at all.

Most common type of star M dwarfs or red dwarfs are the most common type of star in the universe. This discovery could therefore imply that a large number of planets orbiting these stars may also lack atmospheres, and will therefore likely not support life.

The planet named GJ 1252b is slightly larger than our Earth, but is much closer to its star, an M dwarf, than the Earth is to the sun. On a single day on Earth, this planet orbits its star twice.

In order to find out if this planet lacks an atmosphere, astronomers measured infrared radiation from the planet as its light was during a secondary eclipse. In a secondary eclipse, the planet passes behind the star, and hence the planet's light along with the light reflected from its star are blocked.

Scorching temperatures

The radiation revealed the planet's daytime temperatures to be of the order of 2,242 degrees Fahrenheit. This, along with assumed low surface pressure, led the astronomers to believe that GJ 1252b lacks an atmosphere.

The researchers concluded that the planet will not be able to hold on to an atmosphere, even if it had tremendous amounts of carbon dioxide, which traps heat. Even if an atmosphere builds up initially, it would taper off and erode away eventually.

With M dwarf stars having more flares, the likelihood of planets surrounding them closely holding onto their atmospheres goes down further. The lack of atmosphere means that life as we know it is unlikely to flourish.

In Earth’s  solar neighbourhood, there are about 5,000 stars and most of them are M dwarfs. If planets surrounding them can be ruled -out entirely in the search for life based on this discovery, that would leave roughly around 1,000 stars similar to the sun that could be habitable.

For now, however, these can't be ruled out entirely. Nor can we rule out the possibility of a planet far enough away from an M dwarf star such that it retains its atmosphere. We need more research and results as we continue to embark on our search for life elsewhere.

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Brown dwarfs are also known as failed stars. Why? Find out

Brown dwarfs are celestial objects that are too large to be called planets and too small to be called stars. They have. a mass less than 0.075 that of the sun, which is around 75 times the mass of Jupiter. Like stars, brown dwarfs are believed to form from a collapsing cloud of gas and dust. But as the cloud collapses, it does not form an object dense enough at its core to trigger a nuclear fusion. In the case of a star, hydrogen is converted into helium by nuclear fusion. This is what fuels a star and causes it to shine. Brown dwarfs, on the other hand, are not massive enough to ignite fusion. Hence, they are also called ‘failed stars’.

Dimmer and cooler than stars, brown dwarfs are elusive and hard to find. Infrared sky surveys and other techniques have, however, helped scientists detect hundreds of them.

They are believed to be as common as stars in the Universe. Some of them are companions to stars and many are isolated objects.

First discovered in 1995, brown dwarfs were hypothesized in 1963 by American astronomer Shiv Kumar. Despite their name, brown dwarfs are not brown. They appear from deep red to magenta, depending on their temperature.

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