A few weeks ago it was
announced that the Event Horizon
Telescope, a group of eight radio telescopes (on a planetary scale),
provided the first direct visual evidence ever obtained of a Black Hole positioned in the heart of Messier 87, a huge galaxy located in
the nearby Virgo cluster. In a series of six articles in "The Astrophysical Journal Letters",
the image reveals a supermassive Black Hole with a mass equal to 6.5 billion
times that of the Sun and that is 55 million light years from the Earth.
When we talk
about a Black Hole of this mass what are we talking about?
For example the mass of
the planet Earth is 5.97 × 1024 kg (diameter of 12,750 km), while
that of the Sun is 1.99 × 1030 kg (diameter 1.39 × 106
km); the relationship between the values of the 2 masses is easy to remember: 333,333.
The mass of Sgr A* (Black Hole at the center of our
galaxy) is 4.31 × 106 Mo and finally that of the BH of M87 is equal to 6.5 × 109 Mo
(1.29 × 1040 kg ).
From the table, it can
be seen that the BH diameter is directly proportional to its mass, and that if
the Sun became a BH it would have a radius of 2.95 km; multiplying this last
value by the number of solar masses (Mo) we obtain the radius of the
BH.
This is because the Schwarzschild Radius is directly
proportional to its mass:
The Black Hole of M87
which has a mass 6.5 billion solar masses therefore has a RS of about 20 billion km (127 Astronomical Units).
Pluto aphelion is
located at about 49.3 AU (from the Sun), so the Solar System could be
conveniently contained
in the Black Hole of M87.
The Schwarzschild
Radius RS is the distance
at which the escape velocity is c
(speed of light).
Titius-Bode law, an empirical
formula that describes with good approximation the values of the semi-axes
greater than the orbits of the planets of the solar system (expressed in Astronomical Units) and is expressed with the simple formula:
(3n + 4) / 10
where n takes the
values 0, 1, 2, 4, 8, 16, ...
This simple geometric
progression has a nice graphic representation using logarithmic scale:
where a 1 AU we find by definition the Earth and about 10 AU Saturn. As mentioned above, at 127 we can position the event horizon of the Black Hole of M87.
But what is the average density
of a Black Hole?
For Black Holes of "small" dimensions, the average density within the event horizon is incredibly high (see the first table) and at the borders of the Black Hole there are tidal forces greater than a trillion times the gravitational force . However (quite surprisingly) the average density decreases dramatically for the massive Black Holes. A BH of 387 million solar masses would have the average water density and would be comparable to a giant water balloon extending from the Sun to almost Jupiter. A BH of 11 billion solar masses would have the average air density and would be analogous to a giant balloon 2.5 times larger than Pluto's orbit. The average mass density in space itself, however small, may eventually become a low-density BH. If the average density of the Universe corresponds to the critical density of only 5.67 hydrogen atoms per cubic meter, a Hole would form Low density black of about 13.8 billion light years, corresponding to the Big Bang model of the Universe. A BH can use rotation and/or electric charge to avoid collapse. Gravitational forces become negligible for large low density Black Holes.
So you can live in a
large low density BH without even realizing it.
I stop here and let the
reader fantasize ….
AU
Astronomical Unit (Earth - Sun
distance) : 149,597,870 km = 8.5 minutes light
Light
year (distance traveled by light in a year) : 9,460 billion
km = 63,300 AU
Parsec : 3.262 light years = 30,860 billion km = 206,000 AU
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