Split dataframe column into 2 based on row content in R

Question

I'm using tidy census and I have 2 variables for each census tract which makes my data frame look like this:

GEOID	tract	variable	estimate
24005400100	Tract 4001	white_pop	3436
24005400100	Tract 4001	black_pop	98

but I want my variables as separate columns with their estimate as the row content:

GEOID	tract	white_pop	black_pop
24005400100	Tract 4001	3436	98

This is my code to load in the data:

BA_2009_data = get_acs(geography = "tract", 
                  state = "MD",
                  county = "Baltimore County",
                  variables = c(white_pop = "B02008_001", black_pop = "B02009_001"),
                  year = 2009)

I'm fairly new to R, so I am not sure how to work with this.