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Can You Imagine the Size and Mass of Milky Way?

Our ignorance of the Universe around us can be breathtaking at times. For example, the identity of the closest star to the Sun and the length of the day on Saturn are both debatable. On larger scales, we don’t have a good estimate of the mass of our own Galaxy i.e. mass of Milky Way. Indeed, how does one calculate the mass of the Milky Way? Weighing the Milky Way is more than just a game of curiosity. Cosmologists use our Galaxy to test their theories about how dark matter, which is still a mystery, shapes the formation of galaxies. One particular issue is that our home system appears to have too few satellite galaxies in orbit around it, which goes away if our Milky Way is less massive than expected, because lighter central galaxies have a less populated retinue.

Can You Imagine the Size and Mass of Milky Way?

Those dwarf galaxies that we do have are a little surprising in and of themselves. They appear in unusual places, preferring to sit above the poles of the galaxy rather than along its disc, and more of them appear to have ceased significant star formation than similar systems seen elsewhere. The latest data release from ESA’s Gaia satellite, which is busy in mapping and recording the movements of nearly two billion stars, provides an opportunity to see if these mysteries can be resolved by determining the mass of the Milky Way.

Though the majority of the data describes stars in our Galaxy’s main disc, enough have been identified in satellite galaxies that the researchers behind a new paper have been able to determine how these miniature systems are moving in relation to the Milky Way. Because their motion is controlled by the pull of the gravity of Milky Way, we can calculate mass by watching the satellites move and comparing their movements to the esoterically named Phat ELVIS suite of simulated galaxies. In contrast to methods that involve counting stars, we get a value for total mass because we’re measuring the effect of gravity itself, which includes both normal baryonic matter and that pesky dark matter.

In practice, the team compares galaxy population properties such as the speed with which satellites move towards or away from the Milky Way. In an ideal world, they’d be able to calculate how long it has been since each satellite first entered the Milky Way halo. Unfortunately, that can only be determined by going back in time, and because the team lacks a Back to the Future-style DeLorean, they can’t compare this value to simulations. Nonetheless, the findings appear to be convincing, with the Milky Way weighing between 1 and 1.2 trillion solar masses. That’s high enough to keep the missing satellite problem alive.

The physical properties of our home galaxy, the Milky Way, and its evolutionary history are critical to understand the history of galaxy formation throughout the cosmos, as are details such as the efficiency of converting atoms into stars, the development of satellite galaxies such as the Magellanic Clouds, and more. One parameter, the total mass of the Milky Way, is particularly important but remains unknown. It is difficult to measure not only because we are deep within the galaxy, but also because the majority of the mass is in the form of dark matter, which does not radiate.

Current estimates of the total mass of the Milky Way are based on the motions of tidal streamers of gas and globular clusters, both of which are influenced by the galaxy’s gravitational mass, and range from one to several trillion solar masses. Avi Loeb of CfA and his colleague have devised a novel and effective method of estimating the total mass of the Milky Way: modelling the motions of hypervelocity stars, which are thought to be ejected from the galaxy as a result of binary star interactions with the supermassive black hole at our galaxy’s center. So far, more than twenty of these stars have been discovered, moving at speeds of up to 700 kilometers per second and located at distances of more than 150 thousand light-years from the galactic center.

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While the exact mechanism for the formation of these stars is unknown, their orbits are completely determined by the gravitational field of a galaxy, which can be calculated. The astronomers use a nominal travel time of three hundred and thirty million years for these observed hypervelocity stars, which corresponds to their average lifetime when burning hydrogen fuel. When combined with other kinematic data from these stars, the scientists calculate that the mass of the Milky Way that ranges between 1.2 and 1.9 trillion solar masses, which adds significant precision to previous estimates.

Size of Milky Way

Can You Imagine the Size and Mass of Milky Way?

We can’t photograph the spiral structure of the Milky Way Galaxy from the outside because we live within it. We do know, however, that our Milky Way is spiral due to observations made from within our Galaxy. The beautiful spiral galaxy Messier 74 was used to represent this, as it is thought to be similar to our own. Our Galaxy’s disc and center region are easily identified. Above image makes the Milky Way look more like a galaxy and less like the smudge of stars that we see stretching across our night sky. It is possible to imagine what our Milky Way might look like looking down on it from outside.

Although the light year is a widely used unit, astronomers prefer a different unit known as a parsec (pc). A parsec is defined as the distance at which 1 Astronomical Unit subtends an angle of 1 second of arc (1/3600 of a degree). When referring to extremely long distances, we often use a prefix, such as kilo parsecs (kpc), which is equal to 1000 parsecs, or Mega parsecs (Mpc), which is equal to a million parsecs. The Milky Way is approximately 1,000,000,000,000,000,000 km across (approximately 100,000 light years or 30 kpc). The Sun is not located in the center of our Galaxy. It is located about 8 kpc from the center of the Milky Way, on what is known as the Orion Arm of the Milky Way.

The Voyager spacecraft is moving away from the Sun at a rate of 17.3 kilometers per second. It would take more than 450,000,000 years for Voyager to travel 8 kpc to the center of our Galaxy. Even if it could travel at the speed of light, which is impossible due to Special Relativity, it would still take over 26,000 years! It would take Voyager over 1,700,000,000 years to travel the entire length of the Milky Way at 17.3 km/s. It would take nearly a hundred thousand years even at the speed of light!

Discussing the speed of Milky Way means its spin motion. In our Sun’s neighborhood, the Milky Way, an average spiral galaxy, spins at a speed of 130 miles per second (210 km/sec). According to new research, the most massive spiral galaxies spin faster than expected. These “super spirals,” the largest of which weighs roughly 20 times that of our Milky Way, spin at speeds of up to 350 miles per second (570 kilometers per second).

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Facts about Milky Way

  • Our galaxy is warped. The Milky Way is a disc about 1, 20,000 light years across with a central bulge about 12,000 light years in diameter. The disc, however, is not perfectly flat; it is warped as a result of our neighboring galaxies, the Large and Small Magellanic clouds. These two galaxies have been tugging on our galaxy’s matter like a tug of war.
  • It has a halo that is not visible to the naked eye. Our galaxy is composed of approximately 90% dark matter, or matter that cannot be seen, and approximately 10% “luminous matter,” or matter that can be seen with our eyes. This large amount of dark matter creates an invisible halo.
  • The Milky Way galaxy, with an estimated 200 billion stars, is only a medium-sized galaxy. IC 1101 is the largest galaxy known to us, with over 100 trillion stars.
  • Dust and gas make up about 10-15% of the visible matter in the Milky Way, with the rest being stars. The dusty ring of the Milky Way can be seen in the night sky on a clear night.
  • Throughout the history of Milky Way, it has consumed other galaxies in order to achieve its current size and shape. Our galaxy is currently consuming Canis Major Dwarf Galaxy by absorbing the stars of the smaller galaxy into its own spiral.
  • The Milky Way, like larger galaxies, has a supermassive black hole at its center known as Sagittarius A*. This black hole is estimated to have a diameter of 14 million miles, not including the disc of mass that is being drawn into it. This outer disc contains approximately 14.6 million times the mass of our Sun in an orbit similar to that of the Earth!
  • According to scientists, the Universe is approximately 13.7 billion years old, and the Milky Way is approximately 13.6 billion years old. Although the galaxy’s main components formed in the early days of the Universe, the disc and bulge did not fully form until about 10-12 billion years ago.
  • The Milky Way, like everything else in space, is moving. The Earth orbits the Sun, the Sun orbits the Milky Way, and the Milky Way travels through space. The Cosmic Microwave Background radiation, which was left over from the Big Bang, is used as a reference point to calculate the velocity of objects in space. The Milky Way galaxy, which is part of the Local Group of galaxies, is estimated to be moving at 600 km/s or 2.2 million km / hr!
  • While the Milky Way contains up to 400 billion stars, when you look up at night, you can only see 0.0000025 percent of all the stars.
  • Andromeda, one of the universe’s other over 100 billion galaxies, is on a collision course with the Milky Way. The two spiral galaxies will collide in about 5 billion years as they travel at 250,000 miles per hour toward each other.
  • According to calculations using the aluminum-26 isotope mapping method, a supernova explosion occurs in the Milky Way about every 200 years. Aluminum-26 isotopes are typically found in areas where stars are born or die.
  • Every year, approximately 7 new stars are born in the galaxy, according to scientists.
  • The solar system is approximately 30,000 light-years from the galactic center and approximately 20 light-years from the galaxy’s plane.
  • In terms of Cosmic Microwave Background radiation, the Milky Way travels through space at a speed of about 343 miles per second.
  • The galaxy has been dubbed Aakash Ganga in India. This translates as “Ganga of the Heavens.”
  • A star would have to expend enormous amounts of energy to leave the Milky Way. Stars must travel at speeds of one million miles per hour faster than the 600,000 miles per hour that objects already travel around the galaxy.

Facts about the Solar System that will Blow Your Mind

  • There are as many stars in the spiral arms of the galaxy as anywhere else. However, the stars in arms are greater. They burn brighter and die faster. They also shine a light on those around them, making arms more visible.
  • Our solar system takes about 250 million years to complete one galactic year, or one trip around the galaxy, at a speed of 514,000 miles per hour. At that speed, an object would take about 3 minutes to circumnavigate the Earth’s equator.
  • Astronomers must use telescopes that detect radio waves, x-rays, and infrared light when studying the Milky Way. Optical telescopes that only detect visible light are unable to penetrate the dense clouds of dust and gas.
  • Only from within the galaxy can images of the Milky Way be captured. This implies that astronomers have no images of the Milky Way in its entirety. The images you see are either impressions by artists or images of other galaxies.

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