Ejected Star: How fast is fast?

30 years ago, astronomer Jack Hills demonstrated the math behind what has become known as the “Hills Mechanism”. Until this week, it described a celestial event that had never been observed.* But astronomers have always agreed that the physics and math should make what he described possible outcome, if suitable conditions are in play…

Hills explained that under the right conditions, a star might be accelerated to incredible speeds — and might even be flung out of its galaxy. The conditions:

  • A binary star passes close to a black hole, like the one at the center of our galaxy
  • The orbiting stars are caught in the gravity of a black hole, but because of their speed and distance, they are not sucked in.

If conditions are right, one star ends up orbiting the back hole while the other is jettisoned at incredible speed, yet holding onto its mass and shape. All that energy comes from the gravity of the black hole and former momentum of the captured star. [video animation, 20 seconds]

This week, astronomers found clear evidence of this amazing event and traced it back to our galactic center: Five million years ago — as our ancestors learned to walk upright — a star that passed close to the black hole at The Milky Way center was flung away at a stunning 6 million kph. It is traveling so fast, that it is no longer bound to our galaxy or our galactic cluster. It is headed out into the vast intergalactic void.

How fast is fast?

  • Rifle Bullet: Can exceed Mach 3 (2,300 mph)
  • Apollo Rocket: Reached 25,000 mph; Earth escape velocity.
  • Juno Probe: 165,000 mph, a record prior to 2019. (It used Jupiter’s gravity to accelerate)
  • Parker Probe: 213,000 mph (Nov 2019), but will soon reach 430,000 mph

* Prior to this week, astronomers have observed a few stars traveling inexplicably at incredible speeds. But this is the first time, that they have traced the trajectory back to a black hole and the conditions described by Jack Hills.


Stunning 1st image of a Black Hole

Eight of 347 scientists: Their achievement is above the fold in major newspapers

Yesterday (Sep 5, 2019), the Breakthrough Prize Foundation awarded $21.6 million US dollars to the scientists behind a stunning achievement. They imaged a black hole. Although the image was announced and released 5 months ago, the story is still unfolding.

The Breakthrough Prize is funded by Russian-Israeli billionaire Yuri Milner. It is the highest-paying science prize for researchers in life science, math, and physics.

There are many black holes in our galaxy and some small ones in our own galactic “neighborhood”. Yet the EHT team* focused on M87, a black hole in the center of another Galaxy, 55 million light years from our solar system.

This is pretty far, but it is a massive black hole with a bright accretion disk (stuff around the event horizon), and it is orthogonal to our vantage point. How big is the M87 black hole? It is bigger than our entire solar system!

At this unfathomable distance, it is difficult to image anything smaller than an entire galaxy. But by combining data from instruments and math teams around the world, scientists released in April an actual photograph. To be precise, it is the shadow of a black hole, but it clearly shows the accretion disk, event horizon and a hole in the middle. In fact, it shows a perfect, glowing donut.

* The EHT = Event Horizon Telescope

To achieve the implausible, scientists combined data from 8 radio telescopes around the world, including two operated by the European Southern Observatory in Chile (producer of the first video, below). Although data was captured as radio waves, a team of 347 scientists pieced the information together into an actual image. What you see in the paragraph above is not an illustration based on data. It is a genuine photograph.

As you view the 1st video below, you may not feel that it is new. Even with the Big Bang in question, black holes are certain fact, and images have been circulating for years. But—until now—those were all artist’s renderings. There has never been an actual photo of a black hole. This is a first.

A web search turns up many videos about the achievement. Some are less than 2 minutes, and some are 2 hour documentaries. I like these two videos: [1] a 17 minute video documenting the effort to achieve this milestone and clearly explaining the result—and [2] an 11½ minute Ted Talk:

  1. In the Shadow of the Black Hole
  2. Inside the Black Hole That Made History