Help calculating The mass of a Black hole (homework help)

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    Black hole Hole Mass
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Discussion Overview

The discussion revolves around a homework problem related to calculating the mass of a black hole, specifically Cygnus X-1, and understanding the data presented in a lab worksheet. Participants seek clarification on the values in the chart, particularly regarding the mass of the black hole and its companion, as well as the Schwarzschild radius.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about the two different mass values in the chart and seeks help in filling out the worksheet.
  • Another participant questions the labeling of the columns, specifically the meaning of M(BH) and its placement in the chart.
  • There is a suggestion that Cygnus X-1 is a binary system, and M* may represent the mass of the companion star.
  • A participant reflects on the nature of measuring mass, suggesting that it is unlikely to yield an exact value, which may explain the presence of two numbers.
  • One participant concludes that the exercise may not be focused on calculating the mass of the black holes, but rather on understanding the relationship between the black hole and its companion, indicating the need for additional information for accurate calculations.
  • There is mention of the Schwarzschild radius and the need for more data to estimate the radius of the companion star.

Areas of Agreement / Disagreement

Participants exhibit a mix of confusion and clarification regarding the worksheet's data. While there is some agreement on the nature of the binary system and the interpretation of mass values, no consensus is reached on the specific calculations or the purpose of the exercise.

Contextual Notes

Participants note that additional information, such as the distance from the companion and its orbital velocity, is necessary for determining the mass of orbiting objects. There is also uncertainty regarding the labeling of the Schwarzschild radius in the worksheet.

JDenise
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on this lab worksheet i need to fill out the bottom table (the top one is already filled out). I am having trouble understanding The numbers in the first part of the chart. I know RA is right accession and DEC is declination but what I'm not understanding is why there are two different numbers for the mass and why there are 2 numbers in one column. if someone could help me fill out the first column in the bottom chart for Cygnus X-1 that would be amazing, then if you could, explain. i already know the formula for R(s) is 2GM/c^2, but I'm not quite sure how to get the mass for the above numbers. thank you very much !(: P.S. sorry for the dark picture. I know i already have numbers in two boxes but I'm 100% sure they are incorrect so please ignore.
 

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What's the 4th column of the top chart labeled as at the top? I'm having difficulty reading the symbol next to the first M.
 
Drakkith said:
What's the 4th column of the top chart labeled as at the top? I'm having difficulty reading the symbol next to the first M.
M(BH)
 
The 4th column. M(BH) is in the 5th column.
 
Drakkith said:
The 4th column. M(BH) is in the 5th column.
oh, sorry ! its actually an asterisk. that's where i got confused, I've never seen it in a formula like that before .
 
Are these all binary systems? Cygnus x-1 appears to be a binary system. Perhaps M* is the mass of the other stellar object.
 
Drakkith said:
Are these all binary systems? Cygnus x-1 appears to be a binary system. Perhaps M* is the mass of the other stellar object.
i believe so, do you know which values I'd use to plug into the bottom table? I'm not sure why there are two numbers in a column instead of one.
 
Well, why do you think there are two numbers? If I measured the mass of something, would I get an exact value?
 
Drakkith said:
Well, why do you think there are two numbers? If I measured the mass of something, would I get an exact value?
I'd think you'd get something like 14.5 or 16.3 but i know that measuring something that large won't get you an exact number . I'm also guessing that's the reason why is says estimate at the bottom. Thank you, though . I'll need to look at the numbers some more .
 
  • #10
JDenise said:
on this lab worksheet i need to fill out the bottom table (the top one is already filled out). I am having trouble understanding The numbers in the first part of the chart. I know RA is right accession and DEC is declination but what I'm not understanding is why there are two different numbers for the mass and why there are 2 numbers in one column. if someone could help me fill out the first column in the bottom chart for Cygnus X-1 that would be amazing, then if you could, explain. i already know the formula for R(s) is 2GM/c^2, but I'm not quite sure how to get the mass for the above numbers. thank you very much !:)P.S. sorry for the dark picture. I know i already have numbers in two boxes but I'm 100% sure they are incorrect so please ignore.
I do not believe the purpose of this exercise is to determine the mass of the black holes. The fourth column is the mass of the black hole's companion, and the fifth column is the mass of the black hole.

In order to determine the mass of any orbiting object, you need more information. Such as the distance the object is from its companion, and its orbital velocity. Since the masses of the black holes are already given on your worksheet, I can only conclude that calculating the mass of the black holes is not the point of the exercise.

What is not clear is the Rs columns. If the instructor had wanted you to calculate the Schwarzschild Radius of the black hole it should have said RBH on the worksheet. However, in order to estimate the radius of the companion star, more information is also required, such as the surface temperature of the companion star and its bolometric luminosity.

Therefore, I would fill out the worksheet as you had originally intended - calculate the Schwarzschild Radius in both kilometers and miles based upon the given masses of the black holes.
 

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