Star Dust to Star Dust

European Space Agency’s GAIA spacecraft
Stardust to star dust

Are we made of star dust?

Astronomy questions and answers – You have probably heard the expression, “We’re all just star dust” The truth is, depending on the age of the atoms in your body, you could have been stardust several times, by now. The average length of time astronomers estimate it takes atoms discharged during a supernova in the Milky Way to be recycled into a new star or solar system is several billion years.

Supernovae occur very infrequently
Supernovae occur very infrequently about once every century in our Milky Way

How old is the stardust in you?

Figuring out the true age of the atoms in your body is going to be the hard part. Astronomers can give you an estimate for the age of the solar system, the Milky Way, and the universe. The numbers are insignificant to the question since we have no way of knowing where your atoms have been during the estimated 13.798 + or – 0.037 billion years the universe has been in existence. Your atoms could have been part of any number of solar systems and stars, by now.

Star dust is old
Stardust is old

We could narrow the estimate a bit, for you, but we would need to make two assumptions. Firstly, that the Milky Way is the only galaxy your atoms have been a part of during the past. This is most likely the case since astronomers believe galaxies formed relatively soon after the Big Bang. Secondly, that the heavy atoms in your body have only been part of one supernova during their existence. This assumption could possibly be a bit of a stretch, but even being part of one supernova, and returning to be reconsolidated would take several billion years. Once we do this, it becomes easier to narrow the estimate a bit.

A grain of stardust ejected during a supernova can follow a few different roads. It could be flung right out of its host galaxy as part of the galactic wind. Astronomers estimate maybe half of the star dust in the Milky Way presently will eventually follow this road. A percentage of this star dust will certainly be destroyed by the Milky Way’s hot halo, while the remainder will fall back into the galaxy. All most all of the stardust ejected from the galaxy in this way will never become part of a new star or solar system. The whole process is estimated by astronomers to take at least 10 billion years. Since we assume the heavy atoms of your body have only been part of the Milky Way and a single supernova, 10 billion years is an upper limit of the age of the atoms in your body.

The star dust ejected during this supernovae event will probably never become part of a new star
The stardust ejected during this supernovae event will probably never become part of a new star

Dust grains that aren’t ejected from the galaxy during a supernova event will become part of the interstellar medium (ISM). This is the low-density stardust that makes up the space between the stars. The majority of this stardust will also never make it into a new star or solar system. The star dust that does make it back into a new star or solar system will take several billion years to complete the process, as we mentioned above. Several means more than one or two, but not much more, so we’ll say around five billion years it has taken the atoms in your body to become part of the solar system. Astronomers studying the solar system also believe the solar system is around 4.6 billion years old, give or take a few million, and this is close to our estimate of 5 billion years old.

A rough estimate of the age of the stardust in you

There you have a rough estimate of the age of the atoms in your body. From 5 to 10 billion years, given the two assumptions we made. The real point is we are all made of stardust, no matter the age of the atoms in our body.

Click this link to watch a documentary with Neal DeGrasse Tyson on whether we are made of stardust.

Neal DeGrasse Tyson on whether we are star dust

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