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Comment by rwaksmunski | Hacker News Reader

30 billion solar masses, numbers kind of loose the meaning at this scale.

A billion is three groups of three zeroes. So for visualizing I would think of a cubic meter compared to a cubic millimeter.

A grain of sand serves for a cubic millimeter. For the cubic meter you can either visualize a cube that size, or four oil drums, or a small hot tub.

Now for the 30 out front, That’s about 27 which is 3^3 so let’s just size a smaller grain of sand which is only 1/3mm on a side. Maybe table salt would be good.

So a grain of table salt in a small hot tub.

If you perform this thought experiment with actual solar masses, use sufficiently long tongs and wear eye protection.

That's really neat. Thank you.

If they want people to relate to their numbers, they have to use units people understand, and also they need to be accurate about which dimension they are talking about.

If it's mass the correct popular science dumb reporting unit is the blue whale. Ie "The mass of this black hole is almost 3 x 10^35 blue whales"

If it's size, the correct popular science dumb reporting unit is the football field unless it's specifically length, in which case it's acceptable to either go with football field or switch to double-decker bus or blue whale.

Well, most people can't properly understand the scientific notation, as in getting a proper scale of how big one order of magnitude is supposed to be. They may see ^35 and say "oh, so it is like less than 100 of something, meh".

If you doubt that, remember the quarter pounder ads where they made people think 1/4 is kinda more than 1/2 because 4>2...

The point is how are people ever going to get intuition about the numbers if they don't report them in blue whales/football pitches/double decker busses?

At these scales, it really doesn't make much of a difference, as a sibling commenter pointed out.

I was being sarcastic. Pretty sure it's impossible for the vast majority of people (myself definitely included) to gain any kind of intuition for numbers of this scale. I also don't gain any intuition for things by comparing them to a blue whale etc (and I'm not really sure anyone else does either) and find it pretty weird that it seems to be a go-to comparison for science articles in the press.

Armadillos. Now we use armadillos as our unit of measurement.

> 3 x 10^35 blue whales

That’s way more confusing. Most people have never seen a blue whale to scale, let alone can imagine how dense it is. Once you’re at 10^35, why not just increase the exponent and use humans, basketballs or soda cans.

I would imagine that the best scale of measurement would be between 1/100 and 100x.

If the Milky Way is about 1.9T solar masses, then this black hole is about 1.5% the mass of our galaxy.

It’s still a pretty meaningless number, but at least I can look at a picture of the Milky Way and envision 1.5% collapsing into a single object much more easily than I can envision 10^35 of anything.

It is not possible to have an intuition about 1 solar mass, by easily 10 OOM. Adding OOM can't make it less comprehensible.

Not masses, size. The article says size.

In the case of a black hole mass and size (radius) are inextricably and linearly linked. All black holes with a given mass have the same radius (modulo a small effect of angular momentum).

I did a rough calc in: https://news.ycombinator.com/item?id=35361280 When it was pointed out TON618 has ~66 billion solar masses.

But if it is 30 billion times the size of the sun then I think that means it is ~2354000 billion solar masses.

I believe for black holes the volumetric size is a known function of mass. If you exclude the rest of any Lyman-alpha blob present around the black hole.

But it's compared to the sun which has a different size to mass ratio.

So it's a huge difference between 30B times size of the sun and 30B times mass of the sun.

Ah, thank you.

Mass is the only really meaningful measure of a blackhole, as they occupy a spacial singularity, which is to say, the have no measurable size.

The event horizon has a diameter, but that's not the object itself.

Guessing that "size" for black holes can mean mass, volume, or radius. But I'm pretty sure the relationship between those three quantities is well defined and directly proportional, so any way you look at it, this thing is incomprehensibly huge.

30B time the mass of the sun is already huge but 30B times the size of the sun would be much much bigger.

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