The Indian Ocean Has the World's Largest Gravity 'Black Hole' and It's Finally Explained

Earthly Mission (?) ^ | March 11, 2024 | Tamás Varga, sociologist and English major

[SunkenCiv]

If you look at a map of Earth's gravity, you will see a huge blue spot south of India, indicating a region where gravity is weaker than average. This spot is called the Indian Ocean Geoid Low (IOGL), and it is the largest gravity anomaly on our planet.

A gravity anomaly is a difference between the actual gravity measured at a location and the theoretical gravity expected for a perfectly smooth and spherical Earth. But Earth's gravity isn't perfectly uniform and variations in mass distribution beneath the surface cause fluctuations in gravitational pull.

Gravity anomalies can be caused by variations in the density and thickness of Earth's crust, mantle and core. Denser areas have a stronger pull, while less dense regions exert a weaker one. These anomalies affect the shape of the ocean surface, which is not flat but follows the contours of Earth's gravity field. This shape is called the geoid, and it is what we would see if we removed all the effects of tides, winds and currents from the ocean. The geoid is often visualized as a potato-like shape, with bumps and dips corresponding to high and low gravity regions.

The IOGL is one of the most prominent dips in the geoid, covering an area of about 3 million square kilometers, almost the size of India itself. Due to the low gravity there, the sea level over the IOGL is up to 106 m (348 ft) lower than the global average. That means if you were to sail across the IOGL, you would be closer to Earth's center than anywhere else on the ocean.

[FreedomPoster]

+1, perfect.

Stop Making Sense is a great concert movie. I watched a lot of those that first Covid year.

[A_perfect_lady]

Same as it ever was.

[aimhigh]

As I get older, gravity seems to get stronger. There must be a great place with low gravity that would be perfect for retirement.

[one guy in new jersey]

Spitballing here:

Centrifugal force from the spin of the Earth about its poles operates in the opposite direction from gravity.

The missing water in that region has “flowed” (really not, because it’s a steady-state water divot in equilibrium) uphill and radially away from its center because gravity at the center is insufficient to keep it in place compared to normal gravity at the “rim” of the divot.

If the gravity insufficiency were to be eliminated with the snap of the finger, the water would start flowing downhill again, eliminating the water divot.

[one guy in new jersey]

Another question is what is the volume of this water divot, and does that volume fluctuate over time, presumably causing average water levels around the world to rise or fall based on the direction of the change.

[one guy in new jersey]

Also, if the spin of the earth were to stop, on a dime, with the snap of the finger, the water divot would disappear because there would be no more centrifugal force dragging water radially outward/upward from the center of what previously was a water divot.

Admittedly this analysis basically says that the water divot would never have formed at all, despite the gravity anomaly, in the absence of spin-induced centrifugal force.

[one guy in new jersey]

Upon further reflection the divot must be the size it is based on BOTH the size of the gravity deficiency AND the speed of spin (roughly 1,000 miles per hour at sea level).

Be interested to see the math to see which influence predominates.

[BipolarBob]

That sounds counter intuitive to me.

If you think that's bad, stay away from Quantum Physics. There's some freaky stuff going on there.

[Wuli]

Given how the gravitational anomaly results in lower sea levels in the area of the anomaly, I am curious about whether or not those sea lower levels affect the ocean currents, directly in that area and beyond.

[for-q-clinton]

Funny thing is we actually know more about quantum physics than gravity. They still can’t explain how/why gravity works the way it does.

But then I guess they still have some issues explaining how quantum entangled exactly works as well.

[thepoodlebites]

the reason is that higher gravity regions pull ocean water toward them and away from lower gravity regions, causing the latter to have less water and consequently lower sea levels.
—
Haven’t read the article yet but that’s what I was thinking when I read the question? Good question. Gravity sources attract matter, gravity sinks repel.
I wonder if large voids throughout the known universe are regions of dark energy sources which, in theory, would repel matter. Galaxies tend to form in strands and filaments that merge into networks of superclusters (left over from when dark matter dominated the universe)? The 50 mega-parsec voids are particularly interesting.

Here’s a question, is gravity less at the center of the Earth than at the surface? Physics is phun.

[Bubba_Leroy]

Shouldn’t it be higher?

That was my first thought. I suppose the higher gravity areas pull water away from the lower gravity areas?

[SunkenCiv]

Maybe the ISS, but that’s a temporary solution. :^)

[SunkenCiv]

Maybe... they bend to left or right?

[SunkenCiv]

[Tides - NASA Science] The Moon's gravitational pull on Earth, combined with other, tangential forces, causes Earth's water to be redistributed, ultimately creating bulges of water on the side closest to the Moon and the side farthest from the Moon.

NASA/Vi Nguyen

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Earth's tidal bulges don't line up exactly with the Moon's position. Earth's spin carries the tidal bulge forward (Earth's spin being much faster than the Moon's orbital period). This means that the high tide bulges are never directly lined up with the Moon, but a little ahead of it.

NASA/Vi Nguyen

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Twice a month, when the Earth, Sun, and Moon line up, their gravitational power combines to make exceptionally high tides, called spring tides, as well as very low tides where the water has been displaced. When the Sun is at a right angle to the Moon, moderate tides, called neap tides, result. From our view on Earth, these tides coincide with certain lunar phases since they occur when the Moon reaches specific positions in its orbit.

NASA/Vi Nguyen

[rlmorel]

Reading the posts made me think of this! Heh, I love Free Republic!

[SJSAMPLE]

Thx. I read through the article, but I was so confused I missed that.

[IndianChief]

underwater archaeologists are searching for the foundations of the city walls of Dwarka, an ancient city said to have sunk beneath the Arabian Sea, to prove its existence.

There is a documentary on the underwater city of Dwarka, just of the coastal town of modern-day Dwarka. Recently the Indian PM also dived to the ruins underwater. The original city was one of the most holy sites for aancient Hinduism, associated with the Lord Krushna.

[thepoodlebites]

Reading the posts made me think of this! Heh, I love Free Republic!
—
I’m thinking that the force of gravity becomes weakest near the center of the Earth (greatest at the surface). If the Earth was a perfect sphere, gravity would be essentially zero near the center because vector forces on one side would be offset by forces on the opposite side. Thermodynamics dominate near the center where pressure and temperature soars, fueled by gravitational compression and radioactive decay.
dQ = (Cp)dT - dP/ρ. Here, P = ρRT (equation of state).

[rlmorel]

I had to ask Grok to verify, because I think you are correct!