In Brief
The youngest black hole in our galaxy is W49B at a mere 1,000 years old; practically a baby by the universe's standards. Because of the way light-years work, we are looking back in time at it.

Scientists believe that the youngest black hole in the Milky Way is just 1,000 years old. It is located in the center of the supernova remnant W49B, and it wanders through the cosmos some 26,000 light-years away.

It should be noted that scientists are not 100% positive that there is a black hole at the center of W49B. However, there was no neutron star detected (the other object that is typically left behind after a supernova explosion). Since there is no neutron star, scientists have surmised that the W49B remnant surrounds a black hole.

Further analysis is needed for confirmation, but in any case, you can see an image of the remnant below.

Image credit: NASA
Image Credit: NASA

But wait. If the supernova remnant is 26,000 light-years away, how can we see it and simultaneously say that it is only 1,000 years old?

This is a question that popped up recently in relation to an article that we wrote on W49B. And the answer is simple enough (once you have a grasp of how light-years work, anyway). In essence, when looking at the light from this object, scientists estimate that the supernova remnant is just 1,000 years old; however, it took 26,000 years for light from this object to reach us (because it is 26,000 light-years away). So today, this remnant is around 27,000 years old.

But, and this is the important bit, the fact remains: we are seeing the remnant as it was when it was just 1,000 years old (that’s what this image shows: a black hole that is 1,000 years old).

However, space is expanding. This expansion increases the distance between the black hole remnant and Earth. As such, will it take us longer than 26,000 years to see light from this object in the future?

Technically, yes, it will take us a little longer; however, it will only be a tiny bit longer. Ultimately, the expansion of space won’t even add a year to the total amount of travel time.

To break down the facts a little: across an expanse that is 3 million light-years in size (this is known as a “megaparsec”), our universe expands 74 km a second. According to some very rough math, this means that, if a speck of light leaves this object today, by the time that it has traveled across the vast expanse separating it from the Earth, the space between us will have expanded by just about 525,000,000,000 kilometers.

That’s 525 billion km, and it sounds like a lot.

However, a light-year is 9.46 trillion km, so ultimately, over the course of 26,000 years, the rate of expansion is not enough to even add a year on to the travel time. In the end, the expansion of the universe only really comes into play for objects that are amazingly far away (on the scale of millions of light-years).

Standard candles (as they are called) are important tools for scientists when trying to measure distances. Astronomers use a certain kind of star, called Cepheid variable stars, to measure distances throughout the Milky Way.

To put it simply, variable stars are stars that change in brightness.

These stars vary in luminosity (growing bright and then dim) based primarily on how massive they are, where they are located, and how distant they are. Knowing how massive the star is, we can basically determine what the star’s absolute magnitude should be. And comparing those numbers to the apparent magnitude (how bright it looks to us) can give astronomers an accurate idea of how far away an object is.