# Talk:Astronomer tells Wikinews about discovery of closest black hole known so far

Latest comment: 3 years ago by Acagastya in topic Eherpad questions link

## OR

The interview audio and video is uploaded on commons and it is also mentioned in the sister links section.
•–• 23:38, 14 May 2020 (UTC)

### Email requesting clarification

From: Thomas Rivinius To: Agastya

Dear Agastya,

here are my answers:

On 18/05/20 18:58, Agastya Chandrakant wrote:

Hello, sir.

Thank you for discussing the discovery of the nearest black hole with me. There are just a few things we aren't certain we understood properly. Regarding our discussion about the HR6819, I was hoping if you could clarify certain facts about the system.

1. Does the inner star has a gas disk at its equator?

No, it the outer one that is the Be star

2. Is the inner star in the oblate shape?

Again no, this is the outer one.

3. Do we know the rotation velocity at the Equator of any of the stars?

We know the projected rotation, "v sin i" for the inner one, it is about 40km/s. The remaining parameters will have to be worked out in a more detailed study.

4. Which of the two stars rotate more rapidly?

The outer one. Be stars are the most rapidly rotating stars of all.

5. Can you briefly explain what radial-velocity semi-amplitude is?

Semi-amplitude is the difference of maximum - minimum divided by two. "radial velocity" refers to the fact that the stars are in an orbit, meaning from a fixed point of view, they move towards us for a fraction of the time, and recede from us for the remaining time.

Also, could you please have a look at this paragraph and tell me if any part of it is incorrect:
Researchers used the binary mass function to conclude the black hole had a mass of at least 4.2 Solar masses (1 Solar Mass = mass of the Sun). Its companion star, which orbits the black hole in about 40 days, rotates rapidly on its axis. The inner star is classified as a B3 III star, and has a radial velocity semi-amplitude of 61.3 +/- 0.6 km/s. The outer star is classified as a Be star. Be stars are known to rotate around their axis rapidly. Hence, the outer star is not exactly spherical, but instead oblate, bulged at its equator, forming a gas disk around the equator.

Either modify, or completely omit, the second sentence:
"Its companion star, which orbits the black hole in about 40 days, rotates rapidly on its axis."
->
"Its companion star, which orbits the black hole in about 40 days, rotates much less rapidly around its axis than the outer companion."

Best regards,  Rivi

It most definitely requires a better headline.
•–• 21:52, 12 May 2020 (UTC)

For one thing, headlinese generally omits "the". --Pi zero (talk) 22:12, 12 May 2020 (UTC)

## Categories

This article should have La Silla, La Silla Observatory, ESO categories in future.
•–• 22:03, 12 May 2020 (UTC)

## Potential typo

As soon as I type "European" of ESO, my brain thinks "S" is for "Space". Watch out for that typo.
•–• 03:01, 13 May 2020 (UTC)

## Synthesis

This file could be used for the synthesis.
•–• 23:37, 14 May 2020 (UTC)

## Review of revision 4565025 [Not ready]

Is taken care of, as of 20:32, 19 May 2020 (UTC)
•–• 20:32, 19 May 2020 (UTC)

## 310 ± 60 parsec

This appears to be rough numbers, in units of ten parsecs. Which is more than thirty lightyears. Realistically, the equivalent in lightyears should be 1000 ± 200. I'm allowing 1010 ± 195, but probably shouldn't. It's about not claiming to have greater precision than is actually there. --Pi zero (talk) 23:13, 19 May 2020 (UTC)

(The more I think about it, the more uncomfortable I am with the extra precision here... we'll see whether I step it down to 1000 ± 200 by the time the transcript review is complete.) --Pi zero (talk) 23:42, 19 May 2020 (UTC)

## Review of revision 4565634 [Passed]

Most of the questions were formed here: Etherpad link.
•–• 11:08, 3 July 2020 (UTC)