how big is our solar system?

 

The boundary of our solar system

Have you ever wondered where the boundary of our solar system lies is it up until the orbit of pluto the Kuiper belt beyond you may have heard that the voyager spacecraft have already left the solar system their current position putting them well beyond the orbit of pluto but in reality to say they have left the solar system is not really true.

Vehicle determining the boundary

     So how do we define the edge of a solar system?. and following on from that how big can solar systems get let's look first of all at where the voyages are and why some say they have left the solar system astonishingly the voyages which launched in 1977 are still operational today although at reduced capacities their power sources

are radioisotope thermoelectric generators which are great at providing power without the need of solar panels however with every passing year the radioactive material degrades producing less power they are currently operating with about half the power they had when they started meaning a few of the instruments have had to be turned off.

Inquire Deep Space

      What they are currently monitoring is the magnetic field environment of deep space and its interactions with the solar wind of particular interest to scientists is the boundary where the magnetic field and the solar wind of the sun are overcome by interstellar wind this boundary known as the heliopause scientists think that Voyager 1 crossed this boundary in 2012 and Voyager 2 crossed it in 2018 both being the only spacecraft to make it into interstellar space so far.

Found the boundary 

What they found out on their journey is that this boundary is not a spherical ball around the sun but it's rather bubbly and asymmetrical and much like planets facing into the sun with their magnetic fields trailing behind them because of interactions with the solar wind the sun's magnetic field also trails behind against the interstellar wind as the solar system orbits the center of the milky way it travels at over eight hundred thousand kilometers per hour as it moves it passes through what is known as the interstellar medium at relative speeds of eighty thousand kilometers an hour this creates a kind of wind effect on the magnetic field of the sun leaving a tail in interstellar winds wake but as fantastic as the voyager mission is reaching interstellar space is not the same as reaching the edge of the solar system.

The edge of the solar system

The edge of the solar system is defined by gravitational influences a boundary is known as a hill sphere although it should be noted that this is not really a sphere either I'll come to that in a bit a hill sphere is a region around an object

where the gravitational pull of that object overcomes the gravitational pull of anything else, for instance, the moon orbits the earth because it is within the earth's hill sphere it's close enough that the earth's gravitational exertion on the moon dominates the sun's satellites orbiting the moon are within the moon's hill sphere where the moon's gravity at that distance has a greater pull than that of the earth and the sun and everything orbiting the sun is within the sun's hill sphere where the sun's gravity overcomes that of nearby stars this is the true boundary of the solar system.

Local Neighborhood

Now looking at our local neighborhood of stars we find that they are unevenly distributed around us this means that the sun's hill sphere isn't really spherical take the alpha Centauri system for instance it is roughly four light-years away from us yet alpha Centauri contains two sun-like stars so its total gravitational influence will be greater than the sun pushing the boundary of that part of the hill sphere closer to the sun, on the other hand, looking the opposite direction to bernard's star we have a red dwarf star that is six light-years away and much less massive than our star so the sun's gravitational influence would stretch much further in that direction and even if an object is orbiting within the sun's hill sphere near the boundary its orbit is very vicarious the gravity of the sun here is incredibly weak.

Orbit

 The object's orbit would be very slow and the slightest perturbation might knock this object out of orbit that's why astronomers currently think the furthest objects can safely orbit the sun is up to a maximum distance of one light-year even though the sun's hill sphere might stretch out for two to three light-years [Music] so what's out there at that distance anything at all well way beyond the Kuiper belt which is the asteroid belt beyond the orbit of Neptune up to a distance of about one to three light-years is a region known as the Oort cloud.

Oort Cloud

We believe the Oort cloud is a sparsely populated region surrounding the sun containing billions or even trillions of icy bodies we believe that's where a small percentage of the long-period comets come from comets which have orbits of tens to hundreds of thousands of years long to give you some perspective about the

size of this cloud it will take voyager 1 300 years just to reach the beginning of the Oort cloud and potentially 30 000 to 150 000 years to pass through it astronomical distances are simply mind-blowing and remember at this distance we are considered to still be within our own solar system now imagine how many solar systems there are out there which brings me on to the final point. 

Black Holes

How big can solar systems get well it's something we can't know for sure although we can have an educated guess about what it would look like we'll stick strictly to stars for this thought experiment to include black holes would be to include entire galaxies the theoretical limit of a star is around 150 solar masses or 150 times the mass of our sun although there are some stars out there that test this theory like the most massive star that we know of r136a1 which is apparently 300 solar masses now this star resides in a very densely packed cluster so although it is massive its gravity competes with a lot of nearby stars.

this reduces the size of its hill sphere considerably let's say a star of this size was somehow ejected from its local cluster even its local galaxy and finds itself completely alone in space with no other gravitational forces for many light-years in any direction the only other competing mass is other galaxies themselves. that means with nothing competing against it such a solar system could be hundreds to thousands of light-years across comparable in size to a galaxy 

Infinite Distance

Depending on the distances involved in a universe where only this star and a second smaller object exist that the second object could be billions of light-years away and still be in orbit because gravity doesn't care how far away the objects are it will still have an influence on them in such a universe the only escape for the second object from the gravitational pull of the larger object would be to have an infinite distance between the two which isn't possible so there we have it solar systems are already mind-bogglingly large and under the right circumstances they can be far larger still the thought that sticks with me after researching all this is that the universe truly is a fascinating place.

                               ~  Lijo Ferdinand J

              Thanks for Reading all the best and see you next time so you.👍