Is there a massive black hole at the center of our galaxy, the Milky

hello,

In q3 we are given that the radiation differs by a factor of 1000. How do we come to the conclusion that the radiation is lacking by 1000?
Cant it increase by 1000?

Please explain ques 3

Can anyone help with question # 3. Why is E not the correct answer. Thank you!

Would be really grateful if someone could explain why 4d is wrong

VeritasKarishma


I am still confused between answers B and C in the following question.

2. According to the passage, the dynamical evidence referred to in lines 9–10 supports which of the following?

A. Recent assumptions about the velocities of stars
B. Widely held predictions about the amount of matter a black hole will engulf
C. The existence of an extremely dense object at the center of the Milky Way
D. The contention that too much energy is coming from the mass at the Milky Way's galactic center for that mass to be a black hole
E. The conclusion that a compact object of two to three million times the mass of our Sun is too dense to be anything but a black hole

the passage mentions the following
"This dynamical evidence, based on recently confirmed assumptions about the stars' velocities, argues for an extremely compact object with a mass two to three million times the mass of our Sun. Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a black hole"

the underlined portion of the passage mentions the presence of an extremely dense object, reading the second sentence we understand that the dense object referred to previously is at the center of the galaxy ( Milky Way).

The bleu portion of the passage states that the theory mentioned previously supports the assertion that the dense object is too dense to be anything but a back hole. This supports answer E. But some people argue in the forum that "the lack of Energy" mentioned in the passage undermines the conclusion supported previously as a result answer E is wrong. however one can argue that the question is focused on the function of the word "the dynamical evidence" which clearly supports the conclusion mentioned in answer E.

Thank you

Hi GMATNinja and VeritasKarishma,
Can you please explain the meaning of phrase "anything but a black hole".
I inferred it as it could be anything but not black hole, which is different from your reasoning.
Could you please explain the same. Thanks

4. The “widely held predictions” mentioned in line 25 are predictions about the

A. compactness of objects whose mass is millions of times the mass of our Sun
B. velocities of stars orbiting the galactic center
C. amount of matter swirling around the object at the center of the Milky Way
D. amount of matter falling into a theoretical central black hole
E. amount of energy that should be coming from a black hole at the center of the Milky Way



Scientists believe that the amount of
⠀⠀⠀ energy that escapes the black hole should be about
⠀⠀⠀ 10 percent of the matter's rest energy (the energy
⠀⠀⠀ equivalent of its mass according to the equation
⠀⠀⠀ E=mc^2). But when the energy coming from the
(25)  galactic center is compared to widely held predictions
⠀⠀⠀ based on how much matter should be falling into a
⠀⠀⠀ theoretical central black hole, there is a discrepancy
⠀⠀⠀ by a factor of a few thousand.


We are comparing energy coming from the centre with widely held predictions.

Widely held predictions on what? On how much energy should come from the centre based on how much matter should be falling into a central black home.

What do we find? We find that there is a discrepancy by a factor of a few 1000.

The actual energy coming from the centre can be compared with predicted amount of energy only. Only those numbers will be comparable.
How is the prediction made? Based on how much matter should fall into a central black hole.
The idea is that if the centre is a black hole, X amount of matter will fall into it and that will make the centre emit Y amount of energy. When the actual energy being emitted is measured, we find that there is a discrepancy by a factor of a few 1000. So then is it a black hole? We don't know.

Hence (E) is correct.

Hi KarishmaB
That meant if there are any choices that mentioned about "amount of energy", it will be correct?

Hi Everyone,

Since I can see that the only debatable question here is 3 (Diya52 , gmat1393 , legendinthewomb ), I will straight away reason out the options of Q3.

Pertinent lines from the passage to answer the question:
Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a black hole, the relative lack of energy radiating from the galactic center presents a serious problem. A black hole's gravity attracts surrounding matter, which swirls around the black hole, emitting some energy as it is engulfed. Scientists believe that the amount of energy that escapes the black hole should be about 10 percent of the matter's rest energy.

Understanding:
The author presents an 'evidence' that the mass of the galaxy's center is too dense and amount of energy radiating out is less than expected. As this is clearly stated as evidence, this cannot be refuted or argued. Furthermore, they provide a cause behind any radiation of energy, which is a proportional amount of matter being engulfed by galaxy's center. From this, we can easily infer that they had assumed that the mass being engulfed is way much higher.

Working for assumption:
For clear visualization, let us say that the mass engulfed by the galaxy's center which was assumed by the scientists was 1000 Kgs. Thus, the energy radiation must be nearly equal to the energy of the mass of 10Kgs (say 10X). But they could evidence only proportional to 5 Kgs (say 5X). Thus, there is a lack of energy radiations. Hence, what if the assumed engulfed mass was only 500 Kgs, then the realised values would hold true.

Now, let's move to the answer choices.

A) This is exactly matching our prethinking.
B) This is complete opposite of our answer.
(C) and (D) are completely wrong as the mass of galaxy's center is also accounted for.
E) This is a tricky option too. Many would opt for this that what if the energy for a proportion of particular mass of kgs is higher. However, you should pay attention to what the evidence is indicating. THE ENERGY RADIATED OUT OF THE GALAXY's CENTER WOULD STILL BE LESS THAN WHAT THEY WERE EXPECTING. Here, since there is no indication on amount of mass being engulfed, lets assume energy emitted is 50% of the energy of the mass being engulfed. Then per this option, and per our previous 'working for assumption', for 5X energy emissions observed, the mass being engulfed would be 10 Kgs. But does this give us an explanation to low energy radiation- NO.

Hence, A is the correct choice.

Hope this helps !!

Regards,
Parikshit

I am with both of you
can anyone help us out with question number 3

KarishmaB GMATNinja MartyTargetTestPrep

1. What is the term 'relative' referring to? Relative in terms of "energy released relative to energy absorbed" or "energy released actually relative to the predicted release of energy"? How did you decide which one does it imply?

2. I am not clear on what the comparison is established between and how is that determined. There are 2 cases that can arise when we say 'relative' lack of energy. How do we know which one is intended:
a. Same energy in case of assumption and actual but less is being released in actual relative to absorbed energy. Ex. E=1000 and assumed release =10%=100 but actual =5%=50
b. In case of actual, energy is less,i.e, E=500 but in case of assumed, energy is higher, i.e, E =1000 and in both case the amount released =10% thus Actual release= 50 and Assumed release = 100. Here less energy is released relative to assumption.

In both cases actual < assumed but in the latter less is being released purely because less energy is being absorbed so firstly, how is that a problem? Secondly, in this case, probem would be solved by saying "Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high" whereas, in the former case, the correct answer would be something like "Current assumptions about how much energy is released proved to be several thousand times too high". Both are different but seem plausible so how did you choose that we should choose to interpret it by case b?

In the above context is ParikshitAgrawal 's numerical explanation correct?

Experts,

For Q3, the statement in passage says " there is a discrepancy by a factor of a few thousand."

So, it does not confirm that the discrepancy is an increase of decrease from desired value.

Hence only clue to get a correct answer for Q3 is " factor of few thousand" which is stated in B. Hence B should be correct.

Kindly comment.