RELICS FROM THE EARLY UNIVERSE [PRIMORDIAL BLACK HOLE]

RELICS FROM THE EARLY UNIVERSE


Black Holes Are Already Mind-bending Enough. Matter And Energy Compressed Into A Region So Dense That The Escape Velocity Exceed The Speed Of Light Places Where Space And Time Are Tangled Up So Much That Even If You Could Go Faster Than Light Speed, You’d Still End Up At The Singularity.



RELICS FROM THE EARLY UNIVERSE



Astronomers Know Of Two Kinds Of Black Holes In The Universe: Stellar Mass And Supermassive, And How We Get Them Have Been Worked Out Pretty Well. But There’s A Third Class Of Black Hole, One Which Has Never Been Observed Nor Detected Indirectly, And Yet It Could Explain Some Of The Mysteries Of The Universe, Including The Nature Of Dark Matter. Primordial Black Holes.



To Get A Stellar-mass Black Hole, All You Have To Do Is Let A Star With Many Times The Mass Of The Sun Run Out Of Fuel In Its Core. The Star Works Its Way Up Through The Table Of Elements, Fusing Atoms With More And More Protons, Desperately Producing The Energy To Hold Back The Immense Force Of Gravity.



When Their Process Reaches Iron, No Energy Can Be Extracted From The Fusion Process. Fusion In The Core Shuts Off, And The Star Implodes On Itself, With Its Outer Layers Falling Inward At Relativistic Speeds. In Mere Moments, All Of This Mass Is Compressed Into A Region Dense Enough That Nothing, Not Even The Energy Of The Implosion Can Escape.



A Black Hole Is Born. Exactly How Supermassive Black Holes Are Formed Is Still A Bit Of A Mystery. These Can Have Millions Or Even Millions Of Times The Mass Of The Sun, And Form The Hearts Of Many Galaxies Across The Universe.



They’re The End Product Of Merging Stellar-mass Black Holes, Which Feed And Merge, Feed, And Merge Their Way Up To Billions Of Solar Masses. Or Maybe Supermassive Black Holes Can Form All In One Cataclysmic Event, As A Gas Cloud Directly Collapses Into A Single Monster Black Hole, Without Having To Go Through The Whole Star-forming/star-destroying Process First.


RELICS FROM THE EARLY UNIVERSE [PRIMORDIAL BLACK HOLE]



However It Works, Astronomers See Both Stellar And Supermassive Black Holes Across The Universe, And They’ve Worked Out Models Supported By Evidence To Explain How They Form.



Mathematically Speaking, A Black Hole Can Theoretically Be Of Any Mass As Long As It’s Compressed Within A Certain Size. A Black Hole With 10 Times The Mass Of The Sun Would Have An Event Horizon About 59 Kilometres Across. But If You Turned The Sun Into A Black Hole - Which Can’t Happen Naturally - It Would Only Measure 5.8 Km Across. If You Turned The Earth Into A Black Hole, It Would Measure Only 18 Mm Across. And Mount Everest Turned Into A Black Hole Would Be About A Nanometer Across.



Even If The Math Checks Out, Is There Any Theoretical Way That Smaller Black Holes Are Actually Possible? Actually Maybe. And The Idea For This Goes Back To 1974 With Physicist Stephen Hawking.



Hawking Proposed That In The Earliest Moments Of The Universe, Everything Was Kind Of Like A Black Hole, With Matter And Energy Compressed Into An Incomprehensibly Dense Region. Unlike The Universe Today, There Weren’t Vast Differences In Density Where Matter Could Pull Together Into A Single Black Hole.



Looking At The Temperature Differences In The Cosmic Microwave Background Radiation, We Know There Were Regions Of Higher And Lower Density In The Earliest Universe. And Maybe These Over And Under Densities Provided A Spot Where Smaller, Less Massive Black Holes Could Form.



Primordial Black Holes Of All Sizes, From Little More Than A Few Atoms Squeezed Together To Mighty Supermassive Black Holes That Could Form The Seeds For The Even More Massive Black Holes That We See Today. And So Far, These Black Holes Have Evaded Our Detection, Because They’re Just Floating Free Across The Universe.



Drifting Through Space, Disrupting Star Systems And Galaxies With Their Gravity, And Creating An Enormous Amount Of Mass That Doesn’t Interact With Regular Matter Except Through Its Gravity. Does That Sound Familiar? Filling The Universe With Tiny Blobs Of Mass, Which Rarely Interacts With Regular Matter Sounds A Lot Like The Mystery Of Dark Matter.



While Regular Matter Accounts For 5% Of The Universe, Another 27% Seems To Be Dark Matter, Which Dominates The Universe Gravitationally. Astronomers Still Aren’t Sure What Dark Matter Is, But They’ve Mostly Ruled Out That It’s Actually Gravity Acting Strangely At Big Distances, And Are Leaning Towards Some Kind Of Massive, Non-interacting Particle. But One Idea That Just Won’t Go Away Is That Dark Matter Is Actually Explained By Primordial Black Holes.



HOW COULD ASTRONOMERS CONFIRM OR RULE OUT THAT PRIMORDIAL BLACK HOLES ACTUALLY EXIST?


If Primordial Black Holes Really Are Scattered Across The Universe, Making Up Some Or Maybe Even All Of The Missing Matter, How Can Astronomers Find Them? To Fully Account For Dark Matter, Black Holes Would Need To Be Either Asteroid Mass, A Little Less Mass Than The Moon, Or Intermediate-mass Up To 1,000 Times The Mass Of The Sun.



If A Massive Enough Primordial Black Hole Passed Through The Solar System, We’d Certainly Notice The Gravitational Effects As The Planets Were Pulled From Their Orbits. Let’s Hope We Don’t Get To Run That Observation.



But Astronomers Have Come Up With Clever Ideas To Search For Them En Masse Across The Universe. In Early 2020, An International Team Of Astronomers Attempted To Search For Primordial Black Holes Acting As Gravitational Lenses. When A Black Hole Passes In, Between Us And A More Distant Background Object, Its Gravity Acts As A Natural Lens, Distorting The Light From The Distant Object. The Carefully Studied The Light Coming From The Andromeda Galaxy, Which Is 2.5 Million Light-years Away.



They Used The Powerful Subaru Telescope In Hawaii To Take 190 Consecutive Images Of Andromeda. In These Images, There Were 90 Million Individual Stars, Each Of Which Could Have A Black Hole Produce A Lensing Event From Our Perspective. After Two Years Of Data Analysis, Filtering Out All The Noise And Non-gravitational Lens Events From The Data, They Were Only Able To Identify A Single Star That Brightened And Then Dimmed.


RELICS FROM THE EARLY UNIVERSE [PRIMORDIAL BLACK HOLE]



Only One, Possible Primordial Black Hole. And That’s Not Enough Black Holes To Fully Explain Dark Matter. Another Way To Search For Primordial Black Holes Is To Detect When They Disappear. In Addition To Proposing The Idea Of These Tiny Black Holes In The First Place, Hawking Calculated That Black Holes Should Slowly Evaporate Over Vast Periods Of Time.



The Less Massive The Black Hole, The More Quickly It Gives Off Radiation, And The Faster It Loses Mass. In Fact, At This Point In The Age Of The Universe, Any Black Hole Less Than 100 Billion Kilograms Will Have Already Evaporated. As A Black Hole’s Mass Decreases, Its Temperature Increases, And In The End, It’ll Disappear In A Sudden Flash Of Gamma Radiation And Other Particles.



One Of These Particles, For Example, Is The Neutrino. In 2019, Researchers Published A Paper Proposing That The Icecube Neutrino Detector Could Theoretically Detect The Neutrino From An Evaporating Primordial Black Hole During The Last 1,000 Seconds Of Its Life. You Could Also Detect The Flash Of Gamma Radiation. In Fact, One Theory Is That A Class Of Ultra-short Gamma-ray Bursts Are Actually Explosions Of Primordial Black Holes.



Space And Ground-based Observatories Could Detect These Explosions. Astronomers Recently Pored Through 2,700 Hours Of Observations From The High Energy Stereoscopic System And Didn’t Find And Events Yet. Another Way To Search For Primordial Black Holes Is Through Gravitational Waves.



In Fact, In September 2020, Astronomers Announced The Detection Of Two Black Holes Creating A Combined Mass Of 142 Solar Masses. One Of The Black Holes Going Into The Collision Had 85 Times The Mass Of The Sun, Which Is A Very Interesting Number. Exploding Stars Can Create Black Holes Up To 65 Times The Mass Of The Sun. And The Most Massive Stars Can Generate Black Holes Greater Than 120 Solar Masses. But There Shouldn’t Be A Way To Get An 85 Solar Mass Black Hole.



So Where Did This Black Hole Come From? Obviously, It Could Have Been The Result Of A Previous Merger, But Another Intriguing Idea Is That It’s A Primordial Black Hole. If More Of These Collisions Are Detected, It Could Help Astronomers Constrain The Number Of Intermediate-mass Black Holes In The Universe, And Figure Out If They’re A Candidate For Dark Matter.


RELICS FROM THE EARLY UNIVERSE [PRIMORDIAL BLACK HOLE]


Another Possibility Is That You Could Detect The Gravitational Waves Of The Primordial Black Holes That Evaporated At The Beginning Of The Universe Before Even Hydrogen And Helium Were Formed. Primordial Gravitational Waves Caused By Primordial Black Holes.



I’m Sure You’ve Heard The Theory That The Mysterious Planet 9 Could Actually Be A Grapefruit-sized Primordial Black Hole With 5-10 Times The Mass Of The Earth. That Would Nicely Explain Why A Huge Planet In The Outer Solar System Hasn’t Been Discovered Yet. But Dr Avi Loeb And His Collaborators Have Figured Out A Way To Detect Its Presence.



In Theory, This Tiny Black Hole Will Have A Tiny Accretion Disk Of Gas Around It From The Interstellar Medium It’s Feasting On. This Will Heat Up, Melting Nearby Icy Objects In The Kuiper Belt.



In Theory, The Upcoming Vera Rubin Observatory Will Be Able To Detect The Flashes From Icy Objects Getting Too Close To The Black Hole. At This Point, Primordial Black Holes Are Still Entirely Theoretical. But Search The Arxiv Server For Papers And You Get 1,525 Focused On Primordial BlackHoles.




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