WR-104, a threat to Earth?


What is WR-104?

Mainly taken from wikipedia, with irrelevant parts taken out:

WR 104 is a Wolf-Rayet star located 8000 light years from Earth. It is a binary star with a class OB companion. The stars have an orbital period of 220 days and the interaction between their stellar winds produce a spiral “pinwheel” outflow pattern. WR 104′s rotational axis is aligned within 16° of Earth. This could have potential implications to the effects of WR 104′s eventual supernova, since these explosions often produce jets from their rotational poles. It is possible that WR 104 may even produce a gamma ray burst (GRB), though it is not possible to predict with certainty at this time.

WR-104 spiral WR-104 spiral moving

What is a WR star?

Wolf-Rayet stars (often referred to as WR stars) are evolved, massive stars (over 20 solar masses), and are losing their mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s. Wolf-Rayet stars are a normal stage in the evolution of very massive stars, in which strong, broad emission lines of helium and nitrogen (“WN” sequence) or helium, carbon, and oxygen (“WC” sequence) are visible.

What’s the matter with WR-104

The problem with WR-104 is that it is possible for a Wolf-Rayet star to progress to a “collapsar” stage in its death throes: This is when the core of the star collapses to form a black hole, pulling in the surrounding material. This is thought to be the precursor of a long gamma-ray burst(GBR for the rest of the article). That ain’t really a problem itself, the real deal is that the Earth is in the sight of that star and a GBR could possibly be aimed at Earth. Consequences of a GBR hitting Earth are mainly related to global impacts on the biosphere and climate-change triggered by the large dose of radiation.

So the GBR would be pointing at us?

A GBR is not like a laser beam with a clear target. It’s true that the Earth is in the line of “possible” danger, but we have to take in consideration how wide is the GRB. WR 104′s rotational axis is aligned within 16° of Earth and a typical GBR is about 2-20° wide. So, we are not in the comfort zone, but Earth is not a clear target. Remember that we deal with such big distances (8,000 light years), so even 0.1° can make a huge difference in terms of distance. In space, close to Earth can be considered as thousands of kilometers, so we have to keep that in mind.

When will it explode?

I’m not going to lie here just to please people: We don’t know when it is going to explode. Peter Tuthill, professor at the University of Sydney have studied the case since the star was discovered in 2000 and suggest that the star will explode within the next few hundred thousand years. Here’s what he officially says:

The WC spectrum Wolf-Rayet component of the binary should explode sometime within the next few hundred thousand years. To an astronomer, this is the last known stable phase in the life of these massive stars, and it could go anytime. I know of no way to predict this more accurately. The other component, the supergiant O/B star, likely has a much longer fuse than this, and for the rest of this discussion I focus mainly on the WR component.

The WC spectrum analysis is the analysis of the star’s helium, carbon, and oxygen emission. By analyzing this spectrum, you can determine at what stage or phase the star is in. As Tuthill says, it’s the last known stable phase in the life of these massive stars and it could go anytime.

What if it explode?

Well, if it explode tomorrow, we’re safe. The star is 8,000 light years away from Earth and one light year is the distance the light would travel in one year, which is extremely far. So, with gamma rays also traveling at the speed of light, we are looking at 8,000 years for a GRB to hit us. We are safe on that point.

What if it already exploded?

The problem is that when we look at the stars we look back in time. If the star is 8,000 light years away from us, it means what we see now is what the star was looking like 8,000 years ago. So, if the star can explode at any time with the data we have and it’s 8,000 years old data, the star could have already exploded right? Yes, I’m not going to lie to you about that. This means if the star exploded 7,999 years ago, we would know next year. We would know in the case that the burst hit us and it’s very unlikely.

What are your thoughts?

Honestly, I will sleep tonight and you should do the same without worrying too much. Like Phil Plait from badastronomy.com said:

So if it’s less than 10,000 years from exploding and if it blows up as a GRB and if it’s aimed at us and if there isn’t much junk between us and it, then yeah, we may have a problem. But that’s an awful lot of ifs.

There’s way too much ifs to conclude on a theory. It could explode tomorrow, in two hundred thousand years or have already exploded. The GRB might hit Earth as it might not at all and there’s lot of stuff in that 8,000 light years distance that could interfere. The theory is not strong enough to clearly say we are 100% safe and it’s ain’t defined enough to conclude on something. There’s way too much things to worry about in this life, don’t worry about that. Trust me WR-104 is one of the star we know of but there are possibly other stars that could pose a threat to Earth we are just not aware of. I’d say worry about your everyday life, not what’s happening 8,000 years away.

So, is it debunked and we’re safe?

It’s not debunked like the 2012 theory is. I feel confident enough to say you won’t see that GBR in your lifetime, but space is very complex and we have a lot of surprises ahead of us. It’s not worth to worry about WR-104, but it’s a nice thing to be aware of.

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