Brilliant! So simple in retrospect! Anything 240 km/sec slower than us (in the direction of our motion in the milky way) would not be orbiting but would instead be falling. So of course there’s no stars at that speed

Originally shared by Ciro Villa

“Using a novel method and data from the Gaia space telescope, astronomers from the University of Toronto have estimated that the speed of the Sun as it orbits the centre of the Milky Way Galaxy is approximately 240 kilometres per second.

In turn, they have used that result to calculate that the Sun is approximately 7.9 kiloparsecs from the Galaxy’s centre—or almost twenty-six thousand light-years.

Using data from the Gaia space telescope and the RAdial Velocity Experiment (RAVE) survey, Jason Hunt and his colleagues determined the velocities of over 200,000 stars relative to the Sun. Hunt is a Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics, University of Toronto.

The collaborators found an unsurprising distribution of relative velocities: there were stars moving slower, faster and at the same rate as the Sun.

But they also found a shortage of stars with a Galactic orbital velocity of approximately 240 kilometres per second slower than the Sun’s. The astronomers concluded that the missing stars had been stars with zero angular momentum; i.e. they had not been circling the Galaxy like the Sun and the other stars in the Milky Way Galaxy;

“Stars with very close to zero angular momentum would have plunged towards the Galactic centre where they would be strongly affected by the extreme gravitational forces present there,” says Hunt. “This would scatter them into chaotic orbits taking them far above the Galactic plane and away from the Solar neighbourhood.”

“By measuring the velocity with which nearby stars rotate around our Galaxy with respect to the Sun,” says Hunt, “we can observe a lack of stars with a specific negative relative velocity. And because we know this dip corresponds to 0 km/sec, it tells us, in turn, how fast we are moving.”

Hunt and his colleagues then combined this finding with the proper motion of the supermassive blackhole known as Sagittarius A* (“A-star”) that lies at the centre of the Galaxy to calculate the 7.9 kiloparsec distance.

Proper motion is the motion of an object across the sky relative to distant background objects. They calculated the distance in the same way a cartographer triangulates the distance to a terrestrial landmark by observing it from two different positions a known distance apart.

The result was published in Astrophysical Journal Letters in December 2017.”

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7 replies on “Brilliant!”

  1. How can be star missing in solar neighborhood? Stars stays in where they are in which Galaxy they in and also they will disappear forever when life span ends and when stars blow up it means life span of that star is ending other way around you can say is dieying star.

  2. Kenan Yalcinoglu – Two things: 1) it’s not that stars are missing, it’s stars of a specific speed that are missing. There are plenty of stars at all many other speeds. It’s like measuring the speeds of lots of birds in flight and noticing a lack of them are flying at speed zero (aka falling) 2) Stars do not stay in one place in the galaxy. Like planets in our Solar System, stars orbit the Milky Way. Unlike the planets that travel in near-circles, stars orbit in all sorts of crazy patterns. Our Sun will orbit the Milky Way once avery ~250 million years. See – Galactic year – Wikipedia for more detail.

  3. Chris Dolan​​ How can a star loose speed? What I know is scientists knows and believes that planets spins around the stars which means if their is something loose speed or slows down it will be planets that spinning around the stars and moons that spinning around the planets like birds those ones who do flies apart from ostrich and some other flightless birds. Take our star and nearest star to us the Sun as example and does Sun spins around the Earth? The answer is no but long time ago scientists thinks Sun spins around the Earth and way before that scientists fault or thinks Earth it’s in center of the Universe.

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